Exam 2 Review - Pharmacogenetics

1 Exam 2 Review Lecture 10: Pharmacogenetics • Pharmacogenetics o Standard dosing will be effective for most, but not all individuals o Pharmacogenetics is the study of genetic variation that gives rise to specific and idiosyncratic drug responses o An idiosyncratic dr...

1 Exam 2 Review Lecture 10: Pharmacogenetics • Pharmacogenetics o Standard dosing will be effective for most, but not all individuals o Pharmacogenetics is the study of genetic variation that gives rise to specific and idiosyncratic drug responses o An idiosyncratic drug response is a drug response that is unanticipated for the type of drug and its use o Some idiosyncratic variation can be extreme o There are 1 06,000 deaths and 2.2 million serious events per year in the US from adverse drug reactions • Examples of pharmacogenetic effects • Plasma concentrations of Sodium salicylate vs. Isoniazid • Isoniazid o First line drug used to treat tuberculosis o Isoniazid acts by inhibiting formation of the cell wall in mycobacterium o Isoniazid is metabolized by the acetyltransferase activity of NAT2 (N - acetyltransferase 2) which has multiple allelic variants o Genetic variation in acetylator - statu s was first recognized in TB patients taking isoniazid o Variation in the N - acetyltransferase gene divides people into “ Slow acetylators” and “rapid acetylators” o Appropriate dosage depends on whether the patient is a rapid (t1/2 = 1 hour) or slow (t1/2 = 3 hours) acetylator o The rapid allele is dominant § Slow acetylators are homozygous for the slow allele (r/r) § Rapid acetylators may be either homo - or heterozygous (R/R or R/r) o Frequency of NAT2 alleles vary greatly by race and ethnicity Drug Gene(s) impacting response Isoniazid N - acetyltransferase (acetylation) Clopidogrel Cytochrome P450 CYP2C19 Trast uzumab Human Epidermal Growth Factor Receptor 2 Primaquine Glucose - 6 - Phosphate Dehydrogenase Warfarin CYP2C9 + Vitamin K Epoxide Reductase 2 o The frequency of slow acetylator allele of the NAT2 gene is § 90% in the Middle East § 10% in Japan § 72% in the U.S.A. o The means that dosing concerns associated with specific medications may be of greater concern in some racial and ethnic groups than in others • ‘ Clopidogrel (Plavix) o Clopidogrel is indicated for prevention of vascular ischemic events in people with symptomatic atherosclerosis and acute coronary syndrome without ST - segment elevation o Also used with acetylsalicylic acid to prevent thrombosis after pl acement of an intracoronary stent o Clopidogrel is an irreversible inhibitor of the adenosine diphosphate receptor (P2Y) on platelet cell membranes o Grossed over $9 billion in global sales in 2010 o Benefit is observed primarily among smokers o Clopidogrel is a p ro - drug that is metabolized to its active form by cytochrome P450 (CYP) enzymes o The drug is metabolized primarily CYP2C19, which has 25 alleles o The CYP2C19*2 allele has the lowest metabolic activity o Alleles *2 and *3 in the CYP2C19 gene lead to a loss of f unctional protein o Carriers of these alleles fail to convert the prodrug to its active metabolite o In these patients, clopidogrel is inactive and platelets remain reactive • Hawaii vs. Bristol - Myers Squibb o Hawaii recently filed suit against Bristol - Myers Squibb and Sanofi Pharmaceuticals for deceptive business practices for failing to disclose that many individuals will not respond to Plavix (Clopidogrel) o “From 38 percent to 79 percent of Pacific - Islanders and 40 percent to 50 percent of East Asians may respond poorly to Plavix because of a genetic predisposition to inadequately metabolize the drug” - Hawaii Attorney General David Louie • Cytochrome P450 enzyme family o Clopidogrel is typical of a large number of drugs that are metabolized by the cy tochrome P450 (CYP) family of enzymes o CYP proteins metabolize xenobiotic compounds, including most drugs. Unlike Plavix, which is activated by CYP enzymatic activity, most drugs are deactivated by CYP metabolism o CYP enzymes also play a role in the synthesi s of biomolecules including steroid hormones, cholesterol, and bile acids. o The family is highly polymorphic, and the various alleles have variable degrees of enzymatic activity 3 o The Cytochrome P450 (CYP) family of enzymes are primarily membrane - associated monooxygenases that localize to the inner mitochondrial membrane or the endoplasmic reticulum o CYP enzymes metabolize thousands of endogenous & exogenous chemicals o Some CYPs metabolize only one, or very few substrates, such as CYP19A1 (aromatase), while oth ers such as CYP3A4/5 metabolize many substrates • Assay panel for CYP2D6 o CYP2D6 has the greatest phenotypic variability for any of the CYP family members, due to a high degree of genetic polymorphism • CYP2D6 Interactions o Naturally occurring compounds may also induce or inhibit CYP activity o Bioactive compounds found in grapefruit juice have been found to inhibit CYP3A4 - mediated metabolism of certain medications o This can lead to increased bioavailability and, thus, the stro ng possibility of overdosing of drugs metabolized by CYP3A4 o Saint - John's wort induces CYP3A4, but inhibits CYP1A1, CYP1B1 o Tobacco smoking induces CYP1A2 expression o At high concentrations, starfruit juice has been shown to inhibit CYP2A6 o Watercress is a kn own inhibitor of CYP2E1 o Goldenseal, with its two notable alkaloids berberine and hydrastine, has been shown to alter enzymatic activities involving CYP2C9, CYP2D6, and CYP3A4 • Trastuzumab o Trastuzumab ( Herceptin ) is a monoclonal antibody that antagonizes hum an epidermal growth factor o Acts by binding to its receptor; human epidermal growth factor receptor 2 (HER2) o The drug is effective against breast cancer in patients who smoke and whose tumor tissue overexpresses HER2 o Patients whose tumor tissue does not ov erexpress this receptor are not responsive to treatment with trastuzumab o This example is similar to Tamoxifen and the estrogen recepto r • Primaquine o Used in the treatment of relapsing malaria o Mechanism of action is generation of active oxidation products o Causes hemolytic anemia in patients with glucose - 6 - phosphate dehydrogenase (G6PDH) deficiency, which induces lowered levels of reduced glutathione and renders cells more sensitive to oxidative stress o G6PDH deficiency is the most common h uman enzyme defect interestingly, the elevated frequency is due to malarial resistance among carriers (analogous to sickle cell anemia) • Glucose - 6 - phosphate dehydrogenase 4 o Inheritance of G6PDH deficiency is sex - linked and the defect is fully expressed in af fected males but is never transmitted from father to son, but only from mother to son o In females, only one of the two X chromosomes in each cell is active. Consequently, female heterozygotes for G6PDH deficiency have two populations of red cells; deficien t cells and normal cells o G6PDH deficiency can be found in virtually any population, but is most prevalent in individuals of African, Mediterranean, and Oriental ancestry • Warfarin o Warfarin is an anticoagulant that acts as a vitamin K antagonist o Warfarin (Co umadin) is effective and relatively safe for preventing thrombosis and embolism and is the most widely prescribed oral anticoagulant in North America o Warfarin inhibits vitamin K epoxide reductase, an enzyme that recycles oxidized vitamin K to its reduced f orm after it has participated in the carboxylation of prothrombin and factor VII o Warfarin dosage is adjusted to achieve an International Normalized Ratio (INR) of 2 - 3 o Among individuals who do not require Warfarin, the INR is typically around 1 o Under dosing of Warfarin increases risk for a thrombotic event o Overdosing of Warfarin increases the risk of an internal bleed o Establishing the optimal dose is begin in the hospital and continued for ~2 weeks o Warfarin dosing is impacted by pharmacogenetic SNPs, diet & drug - drug interactions • Cytochrome P450 & Warfarin o Warfarin is typical of many drugs that are metabolized by cytochrome P450 enzymes o Warfarin in the circulation is a racemic mixture of R and S forms o Warfarin is metabolized by CYP1A1, CYP1A2, CYP3A4 and CYP2C9 o The S form is 2 - 5 times more active and is metabolized by CYP2C9 o The R form is metabolized primarily by CYP3A4, but also by CYP1A1 and CYP1A2 o CYP2C9 metabolizes warfarin and activity of the enzyme is affecte d by genetic variation in the CYP2C9 gene o Clearance of warfarin is slowed by about 1/3 in individuals who are heterozygous for (possess one copy of) the less functional variant of CYP2C9 o Homozygous individuals (those with two copies of the less functional allele) have a 70% reduction in clearance of warfarin o Variation in the CYP2C9 gene explains 10% of the dose variation between patients • Vitamin K E poxide Reductase & Warfarin o Vitamin K Epoxide Reductase (VKORC1) polymorphisms explain 30% of the dose variati on between patients 5 o High dose haplotypes (group B) make VKORC1 resistant to warfarin inhibition and require higher doses of drug o African Americans are typically more resistant to warfarin (higher proportion of group B haplotypes) o Low dose haplotypes (group A) make VKORC1 sensitive to warfarin inhibition and require lower doses of drug o Asian Americans are typically more sensitive to warfarin (higher proportion of group A haplotypes) • Ethnicity & Warfarin Dosing o CYP2C9 polymorphisms affect primarily Caucasians, as these variants are rare in individuals of African and Asian ancestry o 40% of warfarin dosing depends upon genetic variants in VKORC1 and CYP2C9 o These genetic variants occur at markedly different frequencies in different racial and ethnic grou ps o Clinical findings are that relative to other racial and ethnic groups, particularly Asians, African populations have a higher proportion of Group B haplotypes at VKOR1 and require higher doses of warfarin to achieve the recommended INR ratio between 2 - 3 • Diet & Warfarin Dosing o The mechanism of Warfarin is the depletion of reduced vitamin K, which is necessary for the proper function of the clotting cascade o If a large amount of vitamin K containing items are part of a patient’s diet, the amount of Warfarin needed to prevent unwanted clotting will increase o When on Warfarin, dietary changes that involve increasing or decreasing the intake of foods that are rich in vitamin K (eg: spinach) can be dangerous o If dietary vitamin K is increased substantiall y after an optimal dose of Warfarin has been established, there is an increased risk of thrombosis • Drug - drug interactions & Warfarin Dosing o Drugs that inhibit or induce CYP2C9 impact Warfarin dosing o CYP2C9 inhibitors include Amiodarone, Fluconazole, Isoniazid o CYP2C9 inducers include Rifampin o Inhibition or induction of CYP2C9 activity will increase or decrease the optimal dose of Warfarin required to meet the INR target • Pharmacogenetic testing o Relatively few medical genetic tests are reimb ursable currently o Over 100 drugs have FDA recommendations for PGx testing, including warfarin 6 o Impediments to implementation of testing are multifold o The standards are set by the CMS o Centers for Medicare & Medicare Services o The CMS position on genetic testing has varied greatly • C linical Pharmacogenetics implementation Consortium (CPIC) o An international volunteer group that promotes and facilitates the use of pharmacogenetic tests for patient care Lecture 11: Drug Development and Toxi city • Drug development and safety o Drugs are highly useful treatments for disease o They can also be extremely toxic poisons § used the wrong way or in the wrong population o Structured and rigorous process for developing new treatment to ensure they are effective and safe o Federal laws to ensure safety of food, drugs (both prescription and over the counter) and cosmetics § Supplements excluded § Special laws created for drugs that can lead to compulsive, out - of - control use, both therapeutic and recreational o Drugs are isolated from natural products or synthesized de novo. § Battery of screening tests to see if any potential therapeutic effects. • cellular and molecular assays o Preclinical testing § Does the drug produce beneficial effects in animal models at reasonable dos es § Adverse effects? o Testing in humans § Investigational New Drug application § Cautious, step - by - step testing in larger groups § New Drug Application • Federal Drug Regulations 7 o Morphine and heroin addiction rife by 1900s § heroin lauded (briefly) as a safe alternative to morphine o Opium banned (US) in 1905 o Pure Food and Drug Act in 1906 o Harrison Narcotics Tax Act 1914 o Food, Drug and Cosmetic Act 1938 o Federal Controlled Substances A ct of 1970 o Pure Food and Drug Act in 1906 § accurate labeling o Food, Drug and Cosmetic Act 1938 § evidence of drug safety § detailed labeling of name, dosage and quantity of ingredients § Food and Drug Administration given regulatory power o Durham - Humphrey Amendment 1952 created distinction between prescription and OTC compounds o Kefauver - Harris Amendment 1962 required demonstration of safety in animal studies o Orphan Drug Amendment 1983 incentives for manufacturers to develop treatments for rare diseases o Drug Price Co mpetition and Patent Restoration Act 1984 accelerated approval of generics and extended drug patents o Accelerated Drug Approval 1992 for new drugs for life - threatening conditions o Harrison Narcotics Tax Act 1914 § production, import, manufacture and distributi on regulated § physician prescriptions required o Federal Controlled Substances Act of 1970 § established the Drug Enforcement Administration § classifications “Schedules” • US DEA Schedules o As you go up schedule, it becomes more restrictive o Schedule I controlled substances § - The drug or other substance has a high potential for abuse. § - The drug or other substance has no currently accepted medical use in treatment in the United States. § - There is a lack of accepted safety for use of the drug or other substa nce under medical supervision. o Schedule II controlled substances § - The drug or other substances have a high potential for abuse § - The drug or other substances have currently accepted medical use in treatment in the United States, or currently accepted medica l use with severe restrictions § - Abuse of the drug or other substances may lead to severe psychological or physical dependence. 8 § Except when dispensed directly to an ultimate user by a practitioner other than a pharmacist, no controlled substance in Schedule II may be dispensed without the written prescription of a practitioner, except that in emergency situations, as prescribed by the Secretary by regulation after consultation with the Attorney General, such drug may be dispensed upon oral prescription. With exceptions, an original prescription is always required even though faxing in a prescription in advance to a pharmacy by a prescriber is allowed. No prescription for a controlled substance in schedule II may be refilled. o Schedule III controlled substance s § - The drug or other substance has a potential for abuse less than the drugs or other substances in schedules I and II. § - The drug or other substance has a currently accepted medical use in treatment in the United States. § - Abuse of the drug or other substan ce may lead to moderate or low physical dependence or high psychological dependence. § Except when dispensed directly by a practitioner, other than a pharmacist, to an ultimate user, no controlled substance in schedule III or IV may be dispensed without a wr itten or oral prescription. Such prescriptions may not be filled or refilled more than six months after the date thereof or be refilled more than five times after the date of the prescription unless renewed by the practitioner. A prescription for controlle d substances in Schedules III, IV, and V issued by a practitioner, may be communicated either orally, in writing, or by facsimile to the pharmacist, and may be refilled if so authorized on the prescription or by call - in. Control of wholesale distribution i s somewhat less stringent than Schedule II drugs. o Schedule IV controlled substances § - The drug or other substance has a low potential for abuse relative to the drugs or other substances in schedule III § - The drug or other substance has a currently accepted medical use in treatment in the United States § - Abuse of the drug or other substance may lead to limited physical dependence or psychological dependence relative to the drugs or other substances in schedule III § Control measures are similar to Schedule III. Prescriptions for Schedule IV drugs may be refilled up to five times within a six - month period. A prescription for controlled substances in Schedules III, IV, and V issued by a practitioner, may be communicated either orally, in writing, or by facsimile to the pharmacist, and may be refilled if so authorized on the prescription or by call - in. o Schedule V controlled substances § - The drug or other substance has a low potential for abuse relative to the drugs or other substances in schedule IV 9 § - The drug or other substance has a currently accepted medical use in treatment in the United States § - Abuse of the drug or other substance may lead to limited physical dependence or psychological dependence relative to the drugs or other substances in schedule IV. § No control led substance in schedule V may be distributed or dispensed other than for a medical purpose. A prescription for controlled substances in Schedules III, IV, and V issued by a practitioner, may be communicated either orally, in writing, or by facsimile to t he pharmacist, and may be refilled if so authorized on the prescription or by call - in. • Drug Toxicity o Clinical Selectivity o All substances are toxic at some dose range; some have beneficial effects at some dose range o Need to weigh the ratio of beneficial/therapeutic to toxic/adverse effects o Relative measure of safety is the Therapeutic Index = LD 50 /ED 50 § useful for discussing merits of different treatments o Therapeutic Window is the range of useful doses, LD 50 - ED 50 § provides actual safe vs. toxic doses § a more conservative approach is to use LD 10 /ED 50 • Drug Adverse Effects o Excessive pharmacological effects § Same mechanism • reduce dosage or find a more selective compound • L - DOPA used to treat Parkinson’s disease can result in tardive dyskinesia o Dif ferent mechanisms § Hypersensitivity reactions § Organ systems o Hypersensitivity reactions § Type I immediate • mediated by immunoglobulin e (IgE) • urticaria, atopic dermatitis, anaphylactic shock § Type II cytolytic • mediated by IgG and IgM • hemolytic anemia, thromboc ytopenia • drug - induced lupus erthymatosus § Type III immune complexes • antigen - antigen complexes in vascular endothelium • inflammation, lymphadenopathy, fever (e.g. Steven - Johnson syndrome) § Type IV delayed 10 • sensitized lymphocytes • rashes o Organ Effects § Hemopoietic • bone marrow • often reversible, but may be rapidly fatal § Hepatic • monitor serum transaminase § Nephrotic • can reduce drug clearance § Others • opioids respiratory depression • cardiotoxicity rare but synthetic stimulants • rhabdomyolysis • ra shes § Idiosyncratic • individual genetic differences • Drug Interactions o May be beneficial or harmful § some drug combinations work much better than either drug alone o Pharmaceutical § chemical reactions between drugs before administration • e.g., drug solutions for parenteral administration o Pharmacodynamic § additive, sub - additive, synergistic • can use lower doses of drugs with different mechanisms to increase the overall therapeutic effect and decrease the adverse effects § antagonism o Pharmacokinetic § Absorption • binding to another drug in gut and preventing absorption • altering gastric or intestinal motility • competing for transporters • tetracycline antibiotics are chelated by metals such as iron and aluminum, calcium and magnesium (in antacids) and calcium in dairy products. § Distribution • displacement from plasma proteins • ketoconazole (antifungal), cyclosporine (immune suppressor), vinblastine (anticancer), loperamide (anti - diarrheal) • interference with intestinal bacteria § biotransformation 11 • cytochrome P450 enzymes o dru gs alter transcription of the CYP genes o drugs directly inhibit the enzymes o drugs compete for the enzymes § excretion • changing renal pH • competition for transporter • altering clearance o Polypharmacy and Diet § includes supplements § Polypharmacy • aging o many disorder s, many drugs o complicated with poor education or dementia: can’t track all the drugs and their proper administration • psychiatric o SSRIs increase risk of GI bleeding caused by NSAIDs o treat symptoms § multiple docs — multiple diagnoses — multiple prescriptions § may treat iatrogenic symptoms with new diagnoses and more drugs § Diet • grapefruit juice inhibits CYP3A4 o can cause dangerous elevations in drug concentrations • high tryptamine foods o cause spikes in serotonin levels when taking MAOIs • alcohol o Drug Interactions: Other Factors § Dietary supplements • used for nutrition or medical effects • vitamins § What about CBD? • Heart rhythm medications • Blood - clotting medications • Opioids • Sedative - hypnotics • Antidepressants • Anesthetics (propofol) § Echinacea — tiza nidine, rasagline, caffeine § Evening Primrose oil — warfarin, anti - convulsants § Valerian — muscle relaxants, sedative - hypnotics, pain medications, antidepressants 12 § St. John’s Wort — 500 drug interactions § Melatonin — opioids, muscle relaxants, antihistamines § Kava — 200 drug interactions § Ginseng — warfarin, diabetes, diabetes drugs § Ginko biloba — 260 drug interactions § Garlic — 180 drug interactions § Ginger — 50 drug interactions o Other Factors § Age • infants and the elderly have reduced capacity to metabolize a nd excrete drugs § Disease • diseases of liver and kidney can alter drug metabolism • drugs that have adverse effects on organ systems may be contraindicated in patients with disorders of those systems o heart disease o concussion § Pregnancy and lactation • some drugs may reduce uterine function and lead to miscarriage • drugs may enter the fetus or nursing infant and produce adverse effects o long - term effects on development: teratogens • Pharmacodynamic Drug - Drug Interactions o Additive Combinations § Beneficial : aspirin or ace taminophen + opioid § Harmful : zidovudine + ganciclovir (induction of neutropenia - reduced neutrophils in blood) o Synergistic Combinations § Beneficial : aminoglycoside + penicillin, caffeine + acetaminophen § Harmful : barbiturates + alcohol o Antagonistic Combinations § Beneficial : naloxone in opioid overdose § Harmful : zidoudine + stavudine • Teratogenicity o Greatest risk of fetal abnormalities during 4 th to 10 th weeks § except to brain, which is greatest in 3 rd trimester o Five categories § A clinical evidence of no risk § B possible risk in animal studies, clinical evidence for no risk § C risk found in animal studies, no studies in humans § D risk found in clinical studies § X Contraindicated during pregnancy o Balancing risk 13 § most anti - epileptic drugs produce some risk to fetus • uncontrolled seizures could end the life of both mother and fetus • Exposure to drinking alcohol at an early age predicts an increase in drug and alcohol abuse within the lifespan. Children who start drinking alcohol at age 13 are 4 fold more likely to develop a diagnosis of alcohol abuse or alcoholism. The biological basis of this vulnerability is not yet known. • Teratogens Lecture 12: Tolerance and Dependence • Substance Abuse o Why is this important? § Obviously a timely issue § Great deal of social cost and human suffering o For substance abuse researchers and physicians, the #1 question has become, “How does casual use progress to out - of - control use?” § genetics/epigenetics § socio - environmental milieu • Substance Abuse: Caveats o Addiction is a relapsing, chronic disorder. o Abuse starts early and the younger at onset, the more likely to become addicted. o Abused substances “hijack” the learning and reward system; bypassing the satiety/self - control feedback systems § therefore t his is NOT a moral issue. o There are effective behavioral and medical treatments; involuntary treatment is also effective. o The sooner treatment begins and the longer they stay in, the better. • Hazards o CHICAGO (Reuters) - Prescription painkillers account f or most fatal overdoses from legal drugs in West Virginia and contribute to an exploding problem of overdoses across the United States, U.S. government researchers said on Tuesday. o They said two - thirds of people who died from overdoses of legal pills in th e state had no prescription for the drugs that killed them, suggesting many legal drugs are being diverted for non - medical uses. 14 o "Use and abuse of prescription and particularly narcotic pain medications have increased dramatically in the last 10 to 15 year s," said Aron Hall of U.S. Centers for Disease Control and Prevention, whose study appears in the Journal of the American Medical Association • Opio id Epidemic Causes o 70% of abuse is iatrogenic o Attempted solutions § diversion resistance • crush - proof, add antagonist, aversives, etc. § slowed absorption • Nektar's NKTR - 181 § functional selectivity § peripheral compounds § other receptors o Best solution? § Opioids for short - term use ONLY • Statewide electronic database that collects and monitors outpatie nt prescription dispensation data for schedule II, III, IV and V controlled substances • Managed by the Texas State Board of Pharmacy • Patient care and safety tool - prevents harmful drug interactions, misuse, diversion, and overdose • Prescribers and phar macists are required by Texas state law to check the PMP for every patient, every time before prescribing or dispensing: o Opioids o Benzodiazepines o Barbiturates o Carisoprodol • Predisposing Factors o Age at first use o Family history of substance abuse § genetics , epigenetics and/or behavior patterns o Cultural norms § including perceived norms • college drinking patterns • advertising o Social/group status o Sex/gender o Availability § supply and cost o Patterns of consumption o Comorbidities 15 § depression – anxiety? conduct disorders? § ADHD and mild autism: self - medication § toxic environments (poverty, abuse, neglect, chronic stress) o Family history of alcoholism and age at onset of alcohol use are related to prevalence of alcohol dependence • Tolerance o A reduction in the response to a drug after repeated administration § May take form of a reduction in potency, efficacy, or both o A reduction in the response to a drug after repeated administration § May take form of a reduction in potency, efficacy, or both o Leads users to escalate dosag e to achieve equivalent “high” § or other therapeutic effect o Tolerance does not develop at the same rate for all effects: Tolerance may develop more rapidly to the therapeutic effect than to toxic effects § Decreases the “therapeutic index” of the drug, leadi ng to higher probability of accidental fatality • opioids and respiratory depression § cocaine and cardiovascular events o Tolerance may involve a variety of mechanisms o Tolerance is not limited to drugs of abuse! § steroids, decongestants, antidiuretics, phosphod iesterase inhibitors, etc. • Types of Tolerance o Pharmacokinetic (metabolic) § Decreased response due to changes in distribution or metabolism of a drug after repeated administration • diminished concentration of drug at the site of action: homeostasis § Common mechanism is induction of hepatic metabolism • alcohol • barbiturates • benzodiazepines o Pharmacodynamic § Adaptive changes in target tissue occur with repeated use • diminished response to the same concentration of drug • larger dose needed to produ ce same effect § Common mechanisms • reduced receptor density at the site of drug action o down - regulation of μ - opioid receptors with chronic morphine • uncoupling of receptor from signal transduction pathways • compensatory changes (e.g. up - regulation) in systems m ediating opposing physiological effects § Acute tolerance 16 • Rapid tolerance developing with repeated use on single occasion (or one large dose) o cocaine is often self - administered in a binge pattern, with repeated doses over one to several hours (often limited only by supply) o decrease in response to subsequent doses of cocaine during the binge o in contrast, little tolerance is retained from one binge session to the next o occurs with cocaine, methamphetamine, nicotine, ethanol o mechanism likely desensitization of receptors (and kinetic for ethanol) § Cross tolerance • Tolerance conferred upon one or more other drugs as a result of repeated use of a given drug • involves drugs in the same structural and/or mechanistic category • can be based on similarity of pharmacologic actions, target tissue effects, or metabolic sources of the tolerance o tolerance to a naturally - occurring or synthetic opioid results in cross - tolerance to other opioids o tolerance to ethanol can produce tolerance to other GABA A receptor - mediat ed sedatives and general anesthetics o Learned § A reduction in the effects of a drug due to learned compensatory mechanisms § Behavioral tolerance • skills developed through experience with drug o learning to walk a straight line while intoxicated § Conditioned tol erance (situation - specific tolerance) • based on pairing of drug administration with specific environmental cues related to drug - taking • Subjects become tolerant in environment where received the drug • But NOT in other environments o Only drugs which act on le arning centers • Dependence and Withdrawal o Tolerance reflects the adaptation to repeated presence of drug o Dependence is a state in which the presence of the drug is necessary for normal functioning § develops as a result of an adaptation produced by resetting of homeostatic mechanisms in presence of the drug (ALLOSTASIS) § not directly measurable 17 § can be independent of tolerance o Appearance of a withdrawal syndrome upon cessation of the drug is the only evidence of dependence • Physical and Psychological Dependence o Physical Dependence § specific changes in organ systems (inferred from withdrawal) o Psychological Dependence § cognitive, behavioral, emotional symptoms reported by human subjects (esp. craving) § due to specific changes in what organ system? § principles of physical and psychological dependence are not different — just what organ system is being affected. • Withdrawal o Abnormal signs or symptoms that follow the abrupt discontinuation of a drug, often characterized by feelings of discomfort, distress , and intense craving for the drug. o Signs and symptoms of withdrawal tend to be opposite to the original effects produced by the drug o Signs and symptoms alleviated by re - introduction of the drug or a drug from the same class § Avoidance of withdrawal is a significant determinant of drug - taking. • Drug Classes o Depressants o Stimulants o Opioids o Cannabis o Hallucinogens • Intoxication : Signs and Symptoms 18 • Withdrawal Signs and Symptoms • Addiction — What o HOW tell if a drug is addictive?? § compulsive, out - of - control use • despite negative consequences and/or desire to quit o Question: § What drug(s) is(are) the most addictive/most dangerous? • How would you tell? o What measures to use? o How would you test it? • Addiction — How o How does it happen? § Idea: addiction is due to the development of dependence in the learning/reinforcement areas of brain § Support: abused substances directly produce significant neuroadaptive changes in these brain regions • dopamine involved: ALL abused drugs increase D A levels in these regions § Circumvent regulatory/satiety pathways • “willpower” circumvented • Addiction Mechanism o Addictive disorders can be understood as aberrant modulation of the reinforcement system § dependence in reinforcement systems • metaphorical addictio ns? à similar changes? § what events occur that lead to addiction? • region - specific alteration in neural connectivity o multiple cells — pathways 19 § cellular changes • single cell • Neuroadaptation and Addiction o Large scale changes in brain architecture o Large scale molecular changes § neurotransmitter receptors and transporters • dopamine, glutamate (ionotropic and metabotropic) • DAT, NET, glutamate transport § increased number of synapses § increased number of dendritic spines § altered transcription factors • CREB, ΔFosB • Reinfo rcement and Dopamine o All drugs of abuse increase extracellular dopamine in the nucleus accumbens o Main effects of some drugs at noradrenergic, serotonergic, GABAergic or opioidergic mechanisms o all result in increased DA in the accumbens o rfmt and punishme nt also increase DA in accumbens • Treatment o Pharmacological Therapies § Three Strategies • Maintenance therapy o Controlled doses of a μ agonist are given to substitute for the illegally obtained opioids. o methadone § once daily oral dose — no injection needed § suppre sses withdrawal and reduces craving § patients cheat to get faster, higher rush § community complaints about traffic around centers o LAAM § oral dose 3 times per week § suppresses withdrawal and reduces craving § cardiovascular effects — removed from use in Europe • Antagonist therapy o Used to prevent relapse — cannot cheat o naltrexone § competitively blocks agonist effects § precipitates withdrawal § not often used for opioid abuse — same problems as for alcohol: general anhedonia o antibodies § body’s immune system destroy s compound 20 § can cheat by using drug from different structural class • Combination approach o Use a combination of agonist and antagonist. The agonist reduces craving and the antagonists prevents relapse. o Weak partial agonist achieves the same effect § buprenorphi ne (Suboxone) § tablets contain naloxone to prevent diversion and misuse • The naloxone is destroyed by the liver (first - pass) when taken orally, but if the tablets are crushed and injected, the naloxone will block the effects and may precipitate withdrawal. o Cognitive/Behavioral Therapies § Cognitive/behavioral problem solving § Social support • jobs, housing § Vouchers • reinforcement for abstinence: “clean days” • money, drawings o Brief Interventions/Screening (SBIRT) § Brief Interventions/Screening (SBIRT) • Primary care physicians & Emergency room staff § short surveys or just a couple of questions • give information and/or treatment options § have been very effective in decreasing amounts of smoking and drinking § have been effective at helping addicted patients find treatm ent § reluctance to do so because of social stigma and because if a medical problem is labeled alcohol - related, insurance won’t pay. o Multimodal Therapies § None of the approaches are widely effective on their own. • Combination pharmacotherapy combined with cognitive behavior therapy for periods of 6 months to 2 years has achieved unprecedented success rates. § prison - based programs have reduced recidivism by 75% § Cost? $2000 per prisoner vs. $70,000/year to keep someon e in prison 21 • Treatment o WHY SO LONG? § Combination pharmacotherapy combined with cognitive behavior therapy for periods of 6 months to 2 years has achieved unprecedented success rates. § Typically takes substantial use to become addicted • genetic factors and drug types influence § Scope of the neur oadaptations involved are remarkable • massive neural rewiring in the midbrain and cortex • changes in gene expression • other epigenetic changes § Can someone become truly “unaddicted”? • chronic, relapsing disorder o Why keep harping on this? § HUGE stigma. Huge pres sure to get off methadone/buprenorphine. Lecture 13: Autonomic Pharmacology 1 : Adrenergic Agonists • Autonomic nervous system (ANS) o Contrast with somatic division of the PNS; somatic is under CNS control whereas ANS is independent (autonomous) o Sympathetic a nd parasympathetic divisions: § Afferent and efferent connections to CNS § Parasympathetic: “trophotropic” (leading to growth, rest and digest) § Sympathetic: “ergotropic” (leading to energy expenditure, fight or flight) o Enteric nervous system (ENS): network in walls of GIT involved in motor and secretory activity; has autonomic innervation. • Sympathetic (Thoracolumbar): o Leave CNS via the spinal cord; short fibers (preganglionic) o Terminate in paravertebral chain ganglia, release acetylcholine o Postganglionic (long fibers) innervate cardiac and smooth muscle and glands; main transmitter is norepinephrine (NE) o The adrenal medulla is a modified sympathetic ganglion that releases epinephrine (E), and NE into circulation. • Parasympathetic (Craniosacral): o Leave CNS via cranial nerves (long fibers) (preganglionic) o Terminate in ganglia closely and diffusely associated with target organs, release acetylcholine (ACh). o Postganglionic (short) fibers release acetylcholine • ANS Schematic o This schema tic diagram should be committed to memory, as it will enable prediction of the physiological actions (effects, side - effects, and contraindications) of all drugs you will learn in this section! 22 o The additional information you will need is the following: o Drug receptor action o Autonomic reflex dynamics (next slide) o Drug ADME • Autonomic reflex dynamic: o Autonomic loop: § Peripheral resistance § Heart rate § Contractile force § Venus tone o Only the heart rate has opposing sympathetic and parasympathetic control o Hormonal loop : Renin • Adrenergic junction sites of drug action o Synthesis (Tyrosine hydroxylase) o Storage (VMAT) o Release (VAMPS, SNAPs NET) o Termination of action o Adrenoceptors • Cholinergic junction sites of drug action o Precursor uptake (CHT) o Synthesis (ChAT) o Storage (VAT) o Release (VAMPS, SNAPs)* o Termination of action (acetylcholinesterase) * o Cholinoceptors * o *Sites for clinically useful drugs • Direct - acting adrenergic agonists o Catecholamines : § Epinephrine § Norepinephrine § Dopamine § Dobutamine § Isoproterenol o Non - catecholamin es § Albuterol, LABA § Clonidine § Midodrine § Oxymetazoline § Phenylephrine § Mirabegron • Mechanisms of adrenergic agonists and mimetics o Direct action: bind and activate recepters: § Presynaptic autoreceptors ( α 2) § Postsynaptic receptors ( α 1, β 1, β 2, D1) 23 • Indirect and mixed acting adrenergic agonists o Indirect agonists § Amphetamine § Cocaine o Mixed - acting agonists § Pseudoephedrine • Mechanisms of indirect action o Amphetamine: § Uptake by NET (and other transporters) § Inhibits VMAT (increase intracellular NE) § Reverses NET (and othe r transporters) § Increase extracellular NE o Cocaine : § Inhibits NET (and other transporters) § Increases extracellular NE § Mixed action refers to a combination of direct and indirect actions. • Alpha - and beta - adrenergic agonists o Adrenergic agonists are classifie d as either α - or β - agonists. o Classification is based upon their relative affinity for α - or β - receptors and their subtypes, compared with: § Epinephrine § Norepinephrine § Isoproterenol o Dobutamine and dopamine activate dopamine (D 1 ) receptors in addition to β - receptors. • Sympathetic effectors and adrenorecptors o α , β receptors on cardiac and smooth muscle and glands o α - adrenergic and dopamine (D1) receptors of renal vessels o All receptors with affinity activated via circulation o Don’t forget CNS activation • Adrenergic receptor activation 24 • Alpha - receptors o α 1: cause contraction of: § Vascular smooth muscle, § Iris dilator muscle (radial, not sphincter) § Smooth muscle of urinary bladder o α 2: autoreceptors on symp athetic postganglionic neurons: § cause feedback inhibition of norepinephrine release § on platelets, activation mediates aggregation § in pancreas, mediate inhibition of insulin secretion • Occurs when sympathetic nervous system is activated • Beta - receptors o β 1 cardiac stimulation (plus renin secretion): § Positive chronotrophic effect (increase heart rate), § Positive ionotropic effect (increase contractility), § Positive dromotropic effect (increase cardiac impulse conduction velocity) o β 2 relaxation of smooth m uscle: § bronchial § uterine § vascular o β 2 glycogenolysis o β 3 lipolysis of triglycerides in adipose tissue; relaxation of bladder detrusor o Triglycerides to glycerol and FFA (B3 selective as possible weight loss drugs) • Receptor affinities of catecholamines o Norepinephrine ( α 1 = α 2; β 1 > β 2) o Epinephrine ( α 1 = α 2; β 1 = β 2) o Isoproterenol ( β 1 = β 2 >> α ) o Dopamine (D1 > β 1 > α ) o Dobutamine ( β 1 > β 2 > α ) o Produced by substitutions on the ethylamine side chain (Katzung Fig 9 - 4) • Oversimplifies receptor actions o The foll owing predicts cardiovascular actions of the catecholamines: o Epinephrine α 1+ β 2+ β 1 o Norepinephrine α 1 + β 1 o Isoproterenol β 2+ β 1 o Dopamine β 1+ D1 o Dobutamin e β 1 • E pinephrine efficacy/potency paradox o β 2 adrenergic effects are evident at lower doses o α 1 effects predominate at higher doses partly due to lack of full efficacy at β 2 • Review ANS reflex dynamics : o Norepinephrine activates α 1 - and β 1 to increase: § peripheral resistance ( α 1) 25 § systolic and diastolic blood pressure ( α 1) § reflex bradycardia (parasympathetic opposes chronotropic but not inotropic effect by β 1) o Epinephrine activates α 1, β 1 AND β 2 - receptors and may either increase or decrease diastolic blood pressure and peripheral resistance depe nding on dose. § Low doses decrease due to vasodilation ( β 2) (no reflex) § High doses increase due to vasoconstriction ( α 1) (reflex) § Principle of physiological antagonism (opposition) o Isoproterenol – activates β 1 AND β 2 § Cardiac stimulation ( β 1) WITH vasodila tion ( β 2) (no reflex) • Cardiovascular actions of catecholamines • Clinical applications of sympathomimetics (1): o Shock: septic, cardiogenic, hypovolemic § norepinephrine, dobutamine, dopamine § Management as needed; both α 1 and β 1 actions potentially desirab le § α 1 may compromise tissue perfusion; renal flow is important § β 1 actions increase risk of myocardial ischemia § Dobutamine or dopamine for cardiogenic shock o Dobutamine dilates coronary and renal vasculature; used as a pharmacologic cardiac stress test. • Clinical applications of sympathomimetics (2) o Chronic orthostatic hypotension (neuropathy) § Midodrine; others; orally active α 1 agonist, does not cross BBB § Maintains lower limit for pressure drop attributable to compromised efferent in baroreceptor r eflex § Side effects: supine hypertension, GI disturbance, urinary retention. o Local vasoconstriction ( α 1 effects desired) § Epinephrine: • Hemostasis in oral facial or nasopharyngeal surgery • Combined with local anesthetics to prolong duration o Postprandial hypo tension also an indication for midodrine; usually also due to neuropathy o Midodrine is a prodrug for the active alpha agonist desglymidodrine o Droxidopa: prodrug for norepinephrine via L - amino acid decarboxylase • Clinical applications of sympathomimetics (3) o Nasal decongestion ( α 1 effects desired; temporary only, OTCs) 26 § Phenylephrine: α 1 agonist oral and drops alone and in many combination products. § Pseudoephedrine: Mixed action • Direct α 1 and β receptor agonist • Releaser of norepinephrine • Product control becaus e of diversion to illicit manufacture of methamphetamine o Oxymetazoline: α 1 agonist, drops, spray o All have α 1 or β side - effects as applicable (most likely with oral preparations) o Hypertension; tachycardia, reflex bradycardia, mydriasis, diaphoresis, agita tion o Do not use more than 3 X because of rhinitis medicamentosa ; rebound congestion. o Postprandial hypotension also an indication; usually also due to neuropathy o Midodrine is a prodrug for the active alpha agonist desglymidodrine o Droxidopa: prodrug for norepinephrine via L - amino acid decarboxylase • Clinical applications of sympathomimetics (4) o Asthma and chronic obstructive pulmonary disease (COPD) § Albuterol; others; inhaled selective β 2 agonist • Effective short - acting bronchodilator used prn throughout di sease progression. o LABA: Long acting β agonist (e.g., formoterol, olodaterol). Ultralong acting agonists used only in combination with other drugs for chronic treatment § Asthma: Inhaled corticosteroid plus LABA § COPD: Antimuscarinic plus LABA o Side effects: Minimal because of inhalational route and β 2 receptor selectivity: Tremor, tachycardia, dysrhythmia, hyper or hypotension • Clinical applications of sympathomimetics (5) o Anaphylaxis § Epinephrine § Intramuscular or intravenous for anaphylactic sho ck and other IgE - mediated reactions § Action at α, β 1 , and β 2 receptors confers physiological antagonism of most cardiopulmonary IgE - initiated effects § At risk individuals carry autoinjector • Clinical applications of sympathomimetics (6) o Clonidine § α 2 recepto r agonist (illustrates upstream receptor targeting) § Decreases NE release and CNS sympathetic outflow § Used for resistant hypertension and addiction/withdrawal o Mirabegron § β 3 Receptor selective action useful for lower urinary tract symptoms § Reduces urgency by relaxing detrusor muscle o Amphetamine (abuse potential) 27 § CNS applications: Attention deficit hyperactivity disorder, excessive daytime sleepiness/narcolepsy o Cocaine (abuse potential) § Local anesthetic, hemostatic Lecture 14: Autonomic Pharmacology 2: Adrenergic Antagonists • Adrenergic Receptor Antagonists ( α - Blockers) o Non - selective ( α 1 α 2) § Phenoxybenzamine § Phentolamine o Selective ( α 1> α 2) § Prazosin § Doxazosin § Tamsulosin o Prazosin (first generation for LUTS and BPH) o Doxazosin, tamsulosin, second generation with longer duration of action o Tamsulosin evidently more prostate selective • Adrenergic Receptor Antagonists ( β - Blockers) o Non - Selective § Propranolol § Timolol § Pindolol o β 1 - Selective § Atenolol § Metoprolol o Mixed β and α § Carvedilol § Labetalol • Mechanisms of action of adrenergic antagonists o Direct Action: Occupy active sites to prevent or regulate effect of endogenous transmitter or exogenous agonist: § Presynaptic autoreceptors ( α 2) § Postsynaptic receptors ( α 1, β 1, β 2) o The effect of antagonism on a tissue depends on: § Sympathetic and parasympathetic innervation of the tissue target § Normal or pathological activity of innervating nerves (i.e. sympathetic tone) § The adrenoceptor subtype § Chemical nature of the drug - receptor intera ction o Antagonism allows titration of a neurotransmitters effectiveness at a given site to achieve therapeutic action in disease o This approach typically takes advantage of receptor subtypes and their tissue distributions to achieve specific therapeutic outc omes and minimize side - effects. • Competitive vs non - competitive antagonism o Phentolamine: 28 § Competitive antagonist § The block is surmountable o Phenoxybenzamine § Covalent binding to α receptor § The block is not surmountable § Sustained duration of action • Clinically significant consequences of α blockade o α 1 antagonism: § Relaxation of vascular smooth muscle § Decreased peripheral resistance § Relaxation of α receptor associated smooth muscle of urinary tract o α 2: antagonism: § Release of norepinephrine from feedback inhibition § Inhibition of sympathetic - activated platelet aggregation § Prevent sympathetic inhibition of insulin secretion • Clinically significant consequences of β blockade o Β 1 Antagonism: § Chronotropic effect (decreas ed heart rate), § Inotropic effect (decreased contractility), § Dromotropic effect (decreased impulse conduction) § Renin release (decreased) o β 2 Antagonism: § Bronchial (decreased dilatory effect) § Vascular (decreased dilatory effect) § Metabolic (decreased glycog enolytic effect) o β 3 Antagonism of sympathetic driven lipolysis o Triglycerides to glycerol and FFA (beta 3 selective antagonists may be possible weight loss drugs) • Clinical applications of adrenoceptor antagonists o Pheochromocytoma ( α + β ) o Lower urinary tr act symptoms ( α ) o Hypertension ( α , β , α + β , β / α ) o Angina pectoris ( β ) o Cardiac arrhythmias ( β ) o Glaucoma ( β ) o Migraine (?) • Side - effects/contraindications (1) o α Antagonists alone ( β receptors unopposed) § Tachycardia (via baroreceptor reflex and α 2 block) § Orthostatic hypotension (concern with predisposing conditions) § Miosis (concern in cataract surgery) § Nasal congestion (concern for aggravation of respiratory infection § CNS effects, fatigue, sedation, nause a; inhibited ejaculation • Side - effects/contraindications (2) 29 o β - Antagonist § Heart failure; concern in acute conditions requiring sympathetic drive § Negative chronotropy, dromotropy; concern if a preexisting problem § Withdrawal precipitated effects (e.g., ischem ic damage, infarction) • Chronic therapy with β blockers leads to increase in receptor density • Discontinuation yields catecholamine super sensitivity § Increased airway resistance; concern with asthma or COPD ( β 2 block) § Peripheral artery disease exacerbation ( β 2 block) § Facilitation of hypoglycemia ( β 2, block); masking of symptoms ( β 2 and β 1) § Depression, fatigue, sexual dysfunction (CNS) § Impaired lipid metabolism ( β 3); weight gain o Adage that applies: “You don’t block sympathetic drive to a failing heart” • Side - e ffects: Pharmacodynamic considerations o α 1 receptor selectivity § Nonselective α receptor antagonists (phenoxybenzamine; phentolamine) produce more tachycardia and use is limited to ER or hospital settings. § α selective (prazosin, doxazocin, tamsulosin) used safely in chronic clinical applications. o β 1 receptor selectivity § β 1 selective (metoprolol, atenolol) safer in respiratory disease, diabetes, peripheral artery disease § Selectivity is limited; both selective and nonselective equally efficacious at their β1 receptor targets o Adrenoceptor nonselective § Dual receptor actions (carvedilol, labetalol) obvious advantages; more potent at β than α o Intrinsic sympathomimetic activity (ISA) § Pindolol is a partial agonist with “antagonist - like” effects under high sympathetic drive § Maintains a minimal level of activation of both β 1 and β 2 receptors § Theoretically safer in all clinical applications, but unpopular • Pharmacokinetic considerations o CNS penetration § β blockers differ in lipophilicity; propranolol and metoprolol readily penetrate the CNS; atenolol has little penetration § May effect CNS toxicity or CNS - related therapeutic effects. o Duration of action § Propranolol and metoprolol have short half - lives and are eliminated largely by liver metabolism; bioavailability is variable § Atenolol has a longer half life and is more water soluble, eliminated by kidney; bioavailability is more reliable o May influence choices in context of impaired elimination. 30 Case: Pheo chromocytoma • A 38 - year - old man complains of the recent onset of episodes of headache, nervousness, sweating, a racing heart, and rapid breathing. The episodes last from a few minutes to over an hour and occur several times a day. On physical examination hi s pulse is 86 beats/min, his respiration rate is 24/min, and his blood pressure is 210/110 mm Hg. The patient has no history of hypertension and is taking no medications. He is given oxygen and intravenous labetalol to gradually reduce heart rate and blood pressure. His 24 - h urinary vanillylmandelic acid concentration is elevated, and his epinephrine and norepinephrine levels are several fold above normal. A computed tomography image shows a soft tissue density in the left suprarenal area, but no other abn ormalities and he is placed on phenoxybenzamine, and later metoprolol is added to control high blood pressure until surgery. His blood pressure is gradually reduced to 118/65 mm Hg, and he is started on a high - salt diet to maintain plasma volume. A week l ater he undergoes laparoscopic left adrenalectomy, and his medications are gradually withdrawn. His blood pressure stabilizes at 120/70 mm Hg, and he is discharged after an uneventful recovery on no medication. o Problem: § Adrenal medullary tumor secreting n orepinephrine and epinephrine into circulation leading to pathological sympathetic activity at all adrenoceptive sites. § Increases in HR and BP are episodic and can be elicited by mechanical perturbation § Diagnosis with increase in catecholamines and metabol ites and confirmation with imaging. o Preoperative drugs: § Phenoxybenzamine + propranolol or metoprolol § Goal is to control hypertension and tachycardia and prevent hypertensive crisis during surgery. o Initial ER hypertension management: § Labetalol iv or phentolamine + propranolol • Phenoxybenzamine: o Unsurmountable, long - lasting nonselective α receptor antagonist to lower peripheral resistance and maintain perfusion of vital organs, especially during perturbation of tumor during surgery • P ropranolol or metoprolol o For control of cardiac effects of excess catecholamines o Added only after α block is established to avoid risk of increased vasoconstriction • Lower urinary tract symptoms o Problem: § Reduced ur