Pharmacodynamics Pharmacokinetics.pdf

Medication Administration PHARMACOKINETICS & PHARMACODYNAMICS Student Learning Outcomes Introduction to Medication Administration Differentiate between pharmacokinetic drug interactions and pharmacodynamic drug interactions, including ethnoicodynamics and food interactions. Describe the pharmacodyna...

Medication Administration PHARMACOKINETICS & PHARMACODYNAMICS Student Learning Outcomes Introduction to Medication Administration Differentiate between pharmacokinetic drug interactions and pharmacodynamic drug interactions, including ethnoicodynamics and food interactions. Describe the pharmacodynamic interactions additive, synergistic, and antagonistic. Describes the physiological mechanism of medication action including absorption, distribution, metabolism, and excretion of medications. Overview This week we will start by tracing the path a medication takes to enter the body, how it travels to the site of action, is broken down and excreted Then how the medication produces its effects at the site of action How to safely administer medications following the rights of medication administration Safe delivery of parental medications Introduction Over 11,000 brand name and generic medications available Each medication requires distinct ○ ○ ○ ○ ○ Application Indications Observation for adverse effects Mechanism of actions Some are prescribed for more then one illness The RN must have an understanding of each medication prior to its administration Medication Errors-Safety FIRST Errors and Impact Reducing Errors Introduction Pharmacology – is the study of medication Pharmacotherapy - / Pharmacothetreputics -application of a drug for the purpose of diagnosis, prevention or treatment of suffering (Adams & Urban) Pharmacokinetics – absorption, distribution, metabolism, (biotransformation), excretion Medication: Pharmacokinetics Route: how enter the body Absorption: from site into blood Distribution: from blood into cells, tissues, or organs Action: how a medication acts Metabolism: changed to prepare for excretion Excretion: how they exit the body This knowledge is used when selecting timing, route, risks, and evaluating the response What Are the Benefits of This Info? Assists us to: Optimizes the benefits of the medication Minimizes the harmful effects Select the optimal schedule Adjust the route Educate our clients and their families Enhances our understanding of physiology and pathophysiology Factors That Affect Absorption Absorption – “movement of medication from its site of administration into the blood stream ” Rate of dissolution ○ Drug must first dissolve before it can be absorbed Drugs that dissolve faster are absorbed faster  Repository  Drugs Cross Membranes By: Traveling via channels and pores ○ Must have small ions ○ Sodium & potassium are examples Transport systems – carriers that move drugs from one side of the cell membrane to the other ○ Transportation depends on the structure of the drug molecule Factors That Affect Absorption Absorption dependent on the properties of the drug and on the physiological & anatomical attributes of the surface Surface area ○ ○ The larger the surface area the faster the absorption Anesthesia delivered via the lungs Factors That Affect Absorption Blood flow ○ Drugs absorbed most rapidly from sites with the most blood flow IV – directly into the blood stream  IM – muscles have a good blood supply  Any thing that impedes or enhances blood supply can impact absorption  Heating pad vs. ice pack Factors That Affect Absorption Drug Solubility ○ Lipid soluble drugs can readily cross the cell membranes Ph Partitioning Acids tend to ionize in basic solutions ○ Bases tend to ionize in acidic media Example (Asprin- acidic is absorbed better in the stomach acid then in the lower GI environment-basic) Remaining non ionized increased absorption ○ Routes-Parenteral IV - no barriers to absorption - Immediate & complete absorption - Disadvantages - Incontinent, costly, medication irretrievable Fluid overload Infection Emboli Routes-Parenteral IM ○ Only barrier – capillary wall ○ Drug can easily pass thru tissue ○ Absorption depends on Water soluble will be absorbed more rapidly  Blood flow  ○ Disadvantages Discomfort  Nerve damage  Routes-Parenteral Subcutaneous ○ Nearly identical to IM Oral Barriers 1. Lining of GI tract 2. Capillary wall 3. Absorption pattern solubility stability gastric & intestinal ph. gastric emptying food in GI Other meds special medication coatings Oral Absorption takes place along the GI mucosa either in the stomach or lower GI tract Absorbed meds enter blood stream and go directly to the liver ○ Hepatic first pass effect  ○ Hepatic microsomal enzymes Advantages Easy & inexpensive (relatively)  Safer – potentially reversible  Good choice for senior citizens  Hepatic First Pass Effect First Pass Effect The first-pass effect is a phenomenon of drug metabolism whereby the concentration of a drug is greatly reduced before it reaches the systemic circulation. After a drug is swallowed, it is absorbed by the digestive system and enters the hepatic portal system. It is carried through the portal vein into the liver before it reaches the rest of the body. The liver metabolizes many drugs, sometimes to such an extent that only a small amount of active drug emerges from the liver to the rest of the circulatory system. This first pass through the liver thus greatly reduces the bioavailability of the drug. Alternative routes of administration like suppository, intravenous, intramuscular, inhalational aerosol and sublingual avoid the first-pass effect because they allow drugs to be absorbed directly into the systemic circulation. Oral Disadvantages ○ Variable absorption rate ○ Inactivation of certain medications ○ Requires a conscious & cooperative client ○ Age  Change in gastric pH can affect medication absorption Pharmaceutical Preparation Tablets Enteric coating (do not crush) Sustained release preparations Additional Routes Topical ○ Skin, eyes, ears, nose, mouth, & vagina Inhalation Rectal suppositories – cut in half length wise if needed Quiz-Absorption The patient is receiving multiple medications including one that is used to stimulate gastric peristalsis. The nurse knows that this drug could have what influence on additional oral medication? 1. Increased absorption 2. Reduced excretion 3. Decreased absorption 4. Enhanced distribution Affected by Blood flow to the tissues - Exiting the vascular tissue - to site of action Drug Solubility Lipid soluble drugs are not limited by the barriers that normally limit water soluble drugs (Adams & Urban) Distribution Tissue storage ○ Some tissues have a greater ability to accumulate and store drugs Bone marrow  Teeth  Eyes  Adipose tissue  Distribution Determined: ○ Protein binding Bonds reversible  Albumin – large molecule that remains in the blood stream & therefore amount of med available to the site of action may be limited  Only a few molecules will bind at any one time  Multiple Meds may compete at binding sites – resulting in Over dose  Special Barriers ○ Blood brain & placental barriers Distribution Quiz -Distribution A nursing is administering an oral antibiotic to a client who has an infected leg wound and impaired peripheral circulation to the lower extremities. Which is the nurse’s most important concern about the client’s status when evaluating response to antibiotic? 1. Competence to biotransform the medication 2. Ability to move medication around body 3. Potential to excrete medication from body 4. Capacity to absorb medication into blood stream Metabolism- The body chemically changes the drug molecule Also known as “Biotransformation” “Enzymatic alteration of the drug structure Most often takes place in the liver Multiple enzymes ○ Hepatic microsomal enzymes –  Latest research is focusing on identifying individual characteristics and specific function of these enzymes Consequences of Metabolism Accelerated renal excretion Drug inactivation Increased therapeutic action Activation of “prodrugs” (inactive substance changed to active substance) Increased toxicity Decreased toxicity Factors Impacting Drug Metabolism Age Induction of drug metabolizing enzymes ○ Stimulates liver to breakdown itself faster or this change may affect other medications Hepatic First pass effect Nutritional status Competition between drugs Competition between drugs and food Quiz-Drug Metabolism The nurse is caring for several patients. Which patient will the nurse anticipate is most likely to experience an alteration in drug metabolism? 1. A 3-day old premature infant 2. A 22 year old pregnant female 3. A 32 year old man with kidney stones 4. A 50 year old executive with hypertension Quiz-Metabolism The nurse is care for a patient with hepatitis and resulting hepatic impairment. The nurse would expect the duration of action for most medications to: 1. Decrease 2. Improve 3. Be unaffected 4. Increase Excretion-Removal of drugs from the body Options - glomerular filtration - - Passive tubular reabsorption - - Drugs removed from blood & discarded into the urine Frequently occurs with lipid soluble drugs Active tubular secretion – active pumping of drug into tubular urine Modifiers of Renal Excretion pH – dependent ionization ○ > excretion rate Competition for active tubular transport ○ Competition between drugs for active transport Age ○ Very young immature kidneys – ○ Senior Citizens – decreased effectiveness of kidneys  Creatinine clearance Nonrenal Routes of Drug Excretion Breast milk Bile Lungs Sweat Saliva Quiz- Elimination Mr. T has liver and kidney disease he is administered a medication. The nurse would expect the duration of this mediation for him to: 1. Increase 2. Decrease 3. Remain unchanged 4. Dissipate Pharmacodynamics How a drug changes the body- Medications can only mimic or block normal body functions. They can not confer new functions Plasma Drug Levels Minimum effective concentration ○ Below MEC therapeutic effects of med will not occur Toxic concentration Therapeutic Range Drug half life (t5) Loading & maintenance doses Peak & Trough Medication: Dose Responses Serum half-life: Onset: Time for serum medication concentration to be halved Time it takes after a medication is administered for it to produce a response Peak: Trough: Time at which a medication reaches its highest effective concentration Minimum blood serum concentration before next scheduled dose Duration: Plateau: Time during which the medication is present in concentration great enough to produce a response Blood serum concentration is reached and maintained Time Response Medication: Actions Therapeutic Effect: expected or Side effect: predicted physiological response that a medication causes predictable and often unavoidable secondary effects produced at a usual therapeutic dose Adverse effect: unintended, Toxic effect: develop after undesirable, and often unpredictable severe responses to medication prolonged intake of a medication or when a medication accumulates in the blood because of impaired metabolism or excretion Idiosyncratic reaction: Allergic reaction: Unpredictable. A patient overreacts or underreacts to a medication or has a reaction different from normal Unpredictable. Repeated administration the patient develops an allergic response to it, its chemical preservatives, or a metabolite Medication Interactions Drug may enhance or inhibit drug action ○ Additive - 1+1 = 2  ○ Two drugs from a similar therapeutic class produce a combined summative effect Synergistic effect medications acting together produce a greater effect them each of them alone 1+1 = 3  Medication manufactured as a combination drug Synercid – comb antibiotic – effective against “Staph infections ” Medication Interactions Agonist - medication that produces the same response as the endogenous substance – (actual molecule in the body that produces the desired effect) (some times these substances produce a greater effect then the endogenous substance) partial agonist - medication that produces a weaker effect Antagonist - drug that prevents the agonist from producing the desired effect Medication: Interactions Occur when one medication modifies the action of another A synergistic effect occurs when the combined effect of two medications is greater than the effect of the medications given separately Determinants that Affect Drug Therapy Clinical Factors ○ Age, weight ○ Present health disorder ○ Other disease entities ○ Client drug compliance Administration ○ Drug form ○ Route of administration ○ Multiple drug therapy. ○ Drug interactions Pharmacokinetics ○ Absorption ○ Distribution ○ Metabolism (t1/2) ○ Excretion Pharmacodynamics ○ Onset, peak , & duration ○ Therapeutic range ○ Side effects and adverse effects Pharmacogenitics Medication Administration