Pharmacology in Nursing: Introduction to Drug Therapy PDF

Pharmacology in Nursing Introduction to Drug Therapy Maher Khdour  Grouping of Drugs Names may reflect the conditions for which they are used (e.g. antidepressants) May reflect their chemical characteristics (benzodiazepines) May reflect the effects on body syst...

Pharmacology in Nursing Introduction to Drug Therapy Maher Khdour  Grouping of Drugs Names may reflect the conditions for which they are used (e.g. antidepressants) May reflect their chemical characteristics (benzodiazepines) May reflect the effects on body systems (central nervous system depressants)  Prototype Drugs Individual drugs that represent groups of drugs are called Prototypes May be the first drugs of this group to be ‫ …טוען‬for antibiotics, developed (e.g., penicillin morphine for opioid analgesics)  Drug Names Generic Name is related to the chemical name and is independent of the manufacturer (e.g., sertraline) Trade name is designated and patented by the manufacturer (e.g., Zoloft)  American Drug Laws and Amendments 1938 Food, Drug and Cosmetic Act required proof of safety, authorized factory inspections, established penalties for fraudulent claims‫…טוען‬ FDA: Food Drug Administration  American Drug Laws cont. 1970 Comprehensive Drug Abuse Prevention and Control Act; Title II, Controlled Substances Act Categorized according to potential for abuse Regulated distribution of narcotics and other drugs of abuse DEA charged w/enforcing the Controlled Substances Act  Categories of Controlled Substances Schedule I—not approved for medical use and have high abuse potentials; LSD, heroin, peyote, ecstasy (3,4 methyenedioxy- methamphetamine) Schedule II—used medically. High abuse potential (methadone, meperidine, cocaine, pentobarbital, Tylox)  Categories of Controlled Substances continued Schedule III-less potential for abuse than I and II but may lead to psychological or physical dependence (Vicodin, Tylenol with codeine) Schedule IV-drugs have some potential for abuse (Valium, flurazepam), Clonazepam) Schedule V-contain moderate amounts of controlled substances. An example is Lomotil (atropine and diphenoxylate)  Pregnancy Categories Cat. A-studies in pregnant women failed to show risk to the fetus Cat. B- animal studies have failed to show a risk to the fetus but there are no adequate studies in women Cat. C-animal studies have shown an adverse effect on the fetus, no adequate human studies, benefits may outweigh risks - Bold 1sN. & 54.  Pregnancy Categories cont. Cat. D-positive evidence of human fetal risk Cat. X-animal or human studies have shown fetal abnormalities or toxicity Teratogenic  Pharmacokinetics Involves drug movement through the body to reach sites of action, metabolism, and excretion ‫…טוען‬ ① Specific processes are absorption, ② ⑬ ⑪ distribution, metabolism and excretion slid 8 s S.. It  Pharmacologic Principles Pharmacokinetics ADME – The study of what actually happens to a drug from the time it enters the body until it has left the body a. Absorption movement of a drug from the site of administration b. Distribution transport of a drug in the bloodstream c. Metabolism alteration of a drug in the body d. Excretion elimination of the drug or its compound from the body 0  Pharmacokinetics a. Absorption So The route of administration affects the rate and extent of absorption of that drug Oral Route A. Enteral (GI tract) > - B. Parenteral > - IV and IM Route C. Topical > - skin , addit , The extent of absorption is called BIOAVAILABILITY KEY POINT: not all drug formulations are equally absorbed 0  a. Absorption of oral drugs Factors that affect absorption varies according to the dosage form and route Food or fluids administered with the drug help or hinder absorption food may delay transit to the intestines or, high fat foods may help some fat soluble drugs Dosage formulation tablets, capsules- some dissolve in the stomach, others in the intestine. Certain types are coated to disolve slowly and have timed release. Some types are formulated with small particles that dissolve super fast- ie: micronized glyburide &15581- 9. J - 5 - Gr- ENTERIC COATED : pH dependant dissolve in High pH (>7) in intestine 0  a. Absorption of oral drugs Factors that affect absorption varies according to the dosage form and route Status of the absorptive surface portions of the small intestine may be missing or damaged Rate of blood flow to the small intestine blood flow may be decrease to the intestine in certain instances ie. sepsis, exercise, labor Acidity of the stomach food increases gastric acid production leading to decreased stomach PH. Drugs are formulated to dissolve at a specific PH level. Status of GI motility Fast or slow transit time due to pathology, conditions, or other medications change transit time 0  a. Absorption of oral drugs Some drugs need to be taken on an empty stomach with a full glass of water Other drugs should be taken on a full stomach or with food to enhance absorption or minimize gastric irritation 0  a. Absorption of oral drugs Drugs given by the oral route are absorbed into the mesenteric blood system and go to the liver for biotransformation before traveling on to the general systemic circulation. This is called the FIRST PASS EFFECT Therefore some of the drug is inactivated and not all will be available for use at its intended site of action. Drugs are formulated to account for this difference in availability to the tissues- called (bioavailability) This is why different forms of drugs are not equal 0  CYTO CHROME P450 ENZYME Many different P450 isoforms. They can modify a large number of structurally diverse substrates. One drug may be a substrate for more than one isozyme. Four isozymes are responsible for the vast majority of P450-catalyzed reactions. CYP3A4/5 most drugs CYP2D6 codeine CYP2C8/9 warfarin CYP1A2 Considerable amounts of CYP3A4 are found in intestinal mucosa ( responsible for first-pass metabolism) CYTO Chrome P450 Enzyme >s 5 55. d Hit - a -. 0 0  a. Absorption of parenteral drugs Intravenous Intrathecal (fastest delivery Intraarticular into the blood Intradermal circulation) Transdermal- Intramuscular can be considered parenteral too Subcutaneous 0  a. Absorption of parenteral drugs Parental drugs have no first pass effect Intravenous rapid and 100% bioavailable Avoids problems with stomach acid and intestinal absorption issues Intramuscular not as rapid as IV- will absorb better if there is a good blood supply Some IM medications are in DEPOT form- have a very slow absorption time (even months)- due to the formulation these drugs they should not be given IV- can cause an embolus 0 a. Absorption of topical drugs Avoids the first pass effect Skin (including transdermal patches) Nose Eyes Sublingual Ears Lungs (inhalation) Rectum- can have some first pass effect Vagina 0  a. Absorption of topical drugs Many different formulations of topical drugs May be given for local or systemic effect All have different designs for absorption Gels and ointments- erratic absorption Lotions Patches- absorption at different rates Drops- eyes and ears Nasal sprays- Suppositories Inhalers 0  a. Absorption of oral drugs sublingual and buccal Avoids the first pass effect Absorbed into the highly vascularized tissue under the tongue or between the cheek and the gum- the oral mucosa Bypass the liver Rapidly absorbed 0  a. Absorption The ROUTE of administration affects the rate and extent of absorption ‫…טוען‬ of that drug 0  Bioavailability Is the portion of a dose that reaches the systemic circulation and is available to act on body cells IV administration is 100% bioavailable Subcutaneous administrations has more rapid absorption than does the oral route Mucous membranes allow for rapid and direct absorption into the bloodstream  Distribution Involves the transport of drug molecules within the body After the drug is absorbed into the bloodstream, it is carried by the blood or tissue fluids to its sites of pharmacologic action, metabolism and excretion Protein binding is an important factor in drug distribution  Distribution cont. Drug distribution into the CNS is limited because of the blood-brain barrier Blood-brain barrier is composed of capillaries with tight walls which limits movement of drug molecules into brain tissue Only drugs that are lipid soluble or have a transport system can cross the blood-brain barrier and reach therapeutic concentrations in brain tissue  Distribution cont. Drug distribution during pregancy and lactation is unique as most drugs cross the placenta or in the case of lactation, pass into breastmilk  Metabolism cont. Most drugs are metabolized by the cytochrome P450 enzymes in the liver Liver contains complex system of enzymes, three of which are key in the metabolism of medications/drugs  Metabolism Method by which drugs are inactivated or biotransformed by the body Some drugs yield metabolites that are also active and exert effects on the body until they are excreted (normeperidine) Most drugs are lipid soluble which aids their passage across the cell membrane Pro-drug is inactive convert to active drug in liver (5-10%) Plavix (clopidogrel)  Metabolism cont. Excretion usually is by kidneys. Need to be I water soluble for this to occur. Thus, one function of metabolism is to convert fat soluble medications to water soluble ones..T 8 slos Hepatic drug metabolism or clearance is a major mechanism for terminating drug action and eliminating drug molecules from the body  Cytochrome p450 CYP enzymes catalyze the chemical reactions which ultimately metabolize the medications With chronic administration (greater than 1-3 weeks), some drugs stimulate hepatocytes to produce larger amounts of drug metabolizing enzymes (inducers). Enzyme induction accelerates drug metabolism. Result is that larger doses of the drug may be need for therapeutic effects.  Cytochrome p450 Enzyme inhibition may occur with concurrent administration of two or more drugs that compete for the same metabolizing enzymes (e.g., Dilantin, EES, Tagamet) Oral meds are generally absorbed by the GI tract and carried to the liver. Drug may undergo extensive metabolism leaving little for systemic use. This is called the first pass effect.  Excretion Refers to the elimination of a drug from the body Most are excreted by the kidneys although some are excreted in the bile then the feces  Serum Drug Levels Lab measurement of the amount of a drug in the blood at a particular time Minimum effective concentration (MEC)- must be present before a drug exerts its pharmacologic action on body cells Duration of action-time during which serum drug levels are at or above the MEC (may measure serum drug levels when the drugs have a low therapeutic index)  Pharmacodynamics--Receptors Involves drug actions on target cells and the resulting alterations in cellular biochemical reactions Most drugs chemically bind with receptors at the cellular level Drug-receptor complex initiates physiochemical reactions that stimulate or inhibit cellular functions  Pharmacodynamics-receptors Receptors vary in type, location, number and functional capacity When drug molecules chemically bind with cell receptors, pharmacologic effects result from agonism or antagonism  Pharmacodynamics a) Receptor interactions Key in a lock Drug binds to a specific site on the cell (called a receptor site) and modifies the function of the cell This is the way many drugs work How strong a drug binds to the receptor site is called the AFFINITY for that binding site 0  Pharmacodynamics a) Receptor interactions AGONISTS Drugs that fit well at the receptor site and elicit their own response ANTAGONISTS Drugs that attach to the receptor site and block other drugs from attaching 0  Pharmacodynamics-receptors Agonists-are drugs that produce effects similar to those produced by naturally occurring hormones, neurotransmitters and others. Agonists may accelerate or slow normal cellular processes depending on the type of receptor activated. Antagonists—drugs that inhibit cell function by occupying receptor sites. Not all drugs act on receptors. Examples include: antacids, osmotic diuretics, chelators.  Pharmacodynamics a) Receptor interactions Both Agonists and Antagonists are used in drug therapy – Albuterol inhaler- for asthma is an example of an agonist medicine – Benadryl ( diphenhydramine) is an antagonist. 0  Pharmacodynamics b) Enzyme interactions – The drug alters the enzymes necessary for a certain body function The Ace Inhibitor (Angiotensin converting enzyme inhibitor) class of blood pressure medicines are an example of drugs that exert their action by altering enzyme pathways 0  Pharmacodynamics c) Non-specific interactions – alter the cell structure – alter some crucial cell process Antibiotics are an example of drugs that alter the cell wall or alter the internal function of the bacterial cell 0  : , Adverse drug reactions ADRs Any reaction to a drug that is unexpected and undesirable that occurs at therapeutic doses I Hypersensitivity (allergic) reaction Anaphylactic shock (dangerous) 2. Pharmacologic reactions Predictable, well-known reactions that result in little or no change in patient management -Predictable frequency Usually resolve when the drug is discontinued 0  Contraindications to therapy When the drug will be dangerous for the pt. Allergic to drug Pregnant Impaired liver or kidney function Wrong drug for the problem Many others 0  Pharmacotherapeutics Monitoring Therapeutic index Drug concentration Patient’s condition Tolerance and dependence withdrawal symptoms Interactions Adverse drug effects 0  Pharmacotherapeutics MONITORING Therapeutic index Ratio of safety: the range between a drug’s therapeutic & toxic effects– a LOW therapeutic index means the drug has a greater chance of causing an adverse reaction Drug concentration Drug levels may become toxic if increased i.e.: renal/hepatic patients whose normal mechanisms for metabolism and excretion are compromised Patient’s condition Diseases and and other conditions such as stress and anxiety are just a few examples of conditons that can alter a patient’s response to drug therapy 0  Pharmacotherapeutics MONITORING Tolerance a decreasing response to repeated doses Dependence a physiological or psychological need for a drug Addiction Psychological demand 0  Pharmacotherapeutics Monitoring Interactions Drug interaction issues – j5 Additive effect--smaller doses can be given with same effect ie. Tylenol and Codeine 1+ 1= 2 – Synergistic effect—2 drugs have a greater effect than either drug alone-- HCTZ with enalapril 1+1 >2 – Antagonistic effect--2 drugs have less of an effect than with either drug alone-- antacids with tetracycline- – Incompatibility—2 drugs mixed together and one or more deteriorates---furosemide and heparin 0  Adverse Drug Effects Drug dependency Idiosyncrasy (an abnormal physical reaction by an individual to a food or drug.) Carcinogenicity teratogenicity  Antidotes for Selected Therapeutic Drugs Acetaminophen-mucomyst Digoxin-digibind Beta blockers-Glucagon (increases myocardial contractility) Phenothiazines-benadryl (EPS) Coumadin-vitamin K Heparin-protamine sulfate  Antidotes cont. Benzodiazepines—flumazenil Cholinergics-atropine Calcium channel blockers—calcium gluconate  General Principles of accurate drug administration Six Rights L Right patient 2. Right drug 3. Right dose Y. Right route 5. Right time 6. Right documentation  General Principles cont. Follow the ‘rights’ consistently Learn essential information about each drug Interpret prescriber’s orders correctly Read labels for right medication and concentration  Drug Administration Minimize the use of abbreviations Calculate dosages correctly Measure doses accurately Use appropriate anatomic landmarks to identify sites of IM injections-follow manufacturers recommendations Verify client identity  Drug Administration *****Seek information about the client’s medical diagnoses and condition in relation to drug administration Be especially vigilant with children to avoid errors  Legal Responsibilities Nurse is legally responsible for safe and accurate administration of medications Nurse is expected to have sufficient drug knowledge to recognize and question erroneous orders  Medication Orders Include the full name of the patient Generic or trade name of the drug The dose, the route and frequency of administration Date, time and signature of the prescriber  Routes of Administration Oral Via GI tube Parenteral-IM, IV and sub q Topical Rectal, ophthalmic Otic vaginal  Drug administration cardinal rules Wash hands before giving meds Read chart carefully. If ever in doubt, check the original order Never give medications you are uncertain of unless you have looked them up or have consulted with pharmacy  Drug Administration Cardinal Rules Never give more than 3cc per IM injection Wear gloves with all injections Do not give oral meds if patient is vomiting, sedated, NPO [nil per os] or is unconscious Follow narcotic protocol for signing out of narcotics  Drug selection and dosage Use as few drugs as possible Fixed dose combinations increase compliance Lowest dose with therapeutic effect Follow guidelines but dosages must be individualized ? Drugs with long half-lives may require loading doses then titrated lower maintenance doses  Drug Therapy in Older Adults Physiologic characteristics and pharmacokinetic impact Decreased GI motility—slower absorption Decreased cardiac output—slower absorption from site of administration, decreased distribution to sites of action in tissues Decreased blood flow to liver and kidneys- delayed metabolism and excretion  Drug Therapy in Older Adults Decreased total body water and lean body mass-fat soluble meds stay with patient longer, water soluble drugs are distributed in smaller area, greater risk for toxicity Decreased blood flow to liver-slowed metabolism and detox of drugs  Drug Therapy in Older Adults protein Decreased albumin-decreased availability of protein for binding and transporting. Will also have higher concentration of free active drug. Decreased blood flow to kidneys—impaired drug excretion, potential toxicity  Older Adults Renal Impairment Know baseline renal function Tailor dosages Avoid nephrotoxic medications Be aware of need for additional dosing if patient is receiving renal replacement therapy Maher Khdour