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Pharm Ch. 1
Drug Action: Pharmaceutic, Pharmacokinetic, & Pharmacodynamic Phases
| Question | Answer |
|---|---|
| What 3 phases does a drug taken by mouth go through? | 1. Pharmaceutic (dissolution)2. Pharmacokinetic3. Pharmacodynamic |
| What is the first phase of drug action? | pharmaceutic phase (dissolution) |
| What happens in the pharmaceutic phase? | the drug becomes a solution so that it can cross the biologic membrane |
| What types of drugs do not go through the pharmaceutic phase? | drugs administered parenterally by subcutaneous, intramuscular, or intravenous routes |
| List the 4 processes that occur in the pharmacokinetic phase of a drug reaction. | 1. absorption2. distribution3. metabolism (or biotransformation)4. excretion (or elimination) |
| What happens in the pharmacodynamic phase of drug reactions? | a biologic or physiologic response results |
| What is the most common route of medication adminstration? | mouth (80%) |
| What must solid drugs (such as tablets and capsules) be in the GI tract in order to be absorbed? | they must be in solution: they must disintegrate into small particles to dissolve into a liquid (dissolution) |
| Are tablets 100% drug? | no |
| What are excipients? | fillers and inert substances used in drug preparation to allow the drug to take on a particular size and shape and to enhance drug dissolution |
| What 2 processes occur before tablets are absorbed into the body? | 1. disintegration2. dissolution |
| List some additives that increase the absorbability of the drug? | the ions of potassium (K) and sodium (Na) in penicillin potassium and penicillin sodium |
| Why is penicillin poorly absorbed by the GI tract? | because of gastric acid |
| How is penicillin made to be more absorbable by the GI tract? | by making the drug a potassium or sodium salt |
| Why can infants absorb more penicillin than adults? | because an infant's gastric secretions have a higher pH than those of adults |
| Define disintegration. | the breakdown of a tablet into smaller particles |
| Define dissolution. | the dissolving of the smaller particles in the GI fluid before absorption |
| Define rate limiting. | the time it takes the drug to disintegrate and dissolve to become available for the body to absorb it |
| What type of fluids are drugs both disintegrated and absorbed faster in? | acidic fluids with a pH of 1 or 2 |
| Why are drugs that dissolve primarily in the stomach absorbed more slowly in the elderly and the very young? | because they have less gastric acidity |
| Where do enteric coated drugs disintegrate? Why? | they disintegrate in the alkaline environment of the small intestine; because they resist disintegration in the gastric acid of the stomach |
| Why may enteric coated drugs be delayed in onset? | because they can remain for a long time in the stomach |
| Why should enteric coated tablets and sustained release (beaded) capsules NOT be crushed? | because crushing would alter the place and time of absorption of the drug |
| What may interfere with dissolution and absorption in the GI tract? | food |
| Why should some drugs be taken with food? | 1. because food can enhance the absorption of some drugs2. because some drugs irritate the gastric mucosa and fluids/food may be necessary to dilute the drug concentration and to act as protectants |
| Define pharmacokinetics. | the process of drug movement to achieve drug action |
| List the 4 processes of pharmacokinetics. | 1. absorption2. distribution3. metabolism (or biotransformation)4. excretion (or elimination) |
| When does a nurse apply knowledge of pharmacokinetics? | when assessing the client for possible adverse drug effects |
| Define absorption. | the movement of drug particles from the GI tract to body fluids by passive absorption, active absorption, or pinocytosis. |
| Where are most oral drugs absorbed? | into the surface area of the small intestine through the action of the extensive mucosal villi |
| When is absorption by the mucosal villi in the small intestine reduced? | if the villi are decreased in number because of disease, drug effect, or the removal of the small intestine |
| What types of drugs are destroyed by the digestive enzymes of the small intestine? | protein-based drugs such as insulin and growth hormones |
| Define passive absorption. | absorption that occurs mostly by diffusion (movment from higher concentration to lower concentration); does not require energy for drug to move across membrane |
| Define active absorption. | absorption that requires a carrier such as an enzyme or protein to move the drug against a concentration gradient; energy is required |
| Define pinocytosis. | a process by which cells carry a drug across their membrane by engulfing the drug particles |
| What is the GI membrane composed of? What types of drugs are able to pass readily through the GI membrane? | composed mostly of lipid and protein, so drugs that are lipid soluble pass rapidly through the GI membrane |
| What type of drugs need a carrier (enzyme or protein) to pass through the GI membrane? | water-soluble drugs |
| When can large particles pass through the GI membrane? | if they are non-ionized |
| What type of drugs pass easily and readily through the stomach lining? | weak acid drugs that are less ionized in the stomach, such as aspirin |
| What type of environment does certain drugs such as calcium carbonate and many of the antifungals need in order to achieve greater drug absorption? | an acidic environment; thus food can stimulate the production of gastric acid |
| Why is a large oral dose of penicillin needed? | because hydrochloric acid destroys some drugs such as penicillin G; therefore a larger dose is needed to offset the partial dose loss. |
| What type of drugs do not pass through the GI tract or liver? | parenteral drugs, eyedrops, eardrops, nasal sprays, respiratory inhalants, transdermal drugs, and sublingual drugs |
| What factors can affect drug absorption? | blood flow, pain, stress, hunger, fasting, food, pH |
| Where are drugs that are given IM absorbed faster? | in muscles that have more blood vessels (e.g., the deltoids) than in those that have fewer blood vessels (e.g., the gluteals) |
| Why is drug absorption slower in subcutaneous tissues? | because these tissues have fewer blood vessels |
| Where do drugs go if they do not go directly into the systemic circulation following absorption? | they pass from the intestinal lumen to the liver via the portal vein |
| What happens to some drugs once they reach the liver? | some may be metabolized |
| What happens to acidic drugs in the stomach? | they become un-ionized in the acidic stomach and are then absorbed by the stomach |
| What happens to alkaline drugs in the intestine? | they become un-ionized in the intestine and are then absorbed by the intestine |
| List the characterisitics a molecule must have in order to be absorbed through the stomach? | 1. right molecular weight2. be lipid-soluble3. be non-ionized |
| Define first-pass effect. | the process in which the drug passes to the liver first |
| Give some examples of drugs with first-pass metabolism. | 1. warfarin (Coumadin)2. morphine |
| Why is lidocaine and nitroglycerin not given orally? | because they have extensive first-pass metabolism and therefore most of the dose would be destroyed |
| Define bioavailability. | the percentage of the administered drug dose that reaches the systemic circulation |
| When does bioavailability occur for drugs given orally? | after absorption and hepatic drug metabolism |
| What is the percent of bioavailability for the oral route of drug administration? | always less than 100% |
| What is the percent of bioavailability for the IV route of drug administration? | usually 100% |
| Oral drugs that have high first-pass hepatic metabolism may have a bioavailability of only _____ to _____ % on entering the systemic circulation. | 20-40% |
| For oral drugs that have a high first-pass metabolism, what must be done in order to obtain the desired drug effect? | the oral dose should be 3 to 5 times larger than the dose given via IV |
| List the factors that alter bioavailability. | 1. the drug form (e.g., tablet, liquid)2. route of administration (e.g., IV, oral)3. GI mucosa motility4. food and other drugs5. changes in liver metabolism caused by liver dysfunction or inadequate hepatic blood flow |
| What happens to the bioavailability of a drug if the person has decreased liver function or a decrease in hepatic blood flow? | can increase the bioavailability, but only if the drug is metabolized by the liver |
| What happens to the bioavailability of a drug if an oral drug is rapidly absorbed? | it can increase the bioavailability of the drug and cause an increase in drug concentration; drug toxicity may result |
| What happens to the bioavailability of a drug if an oral drug is slowly absorbed? | it can limit the bioavailability of the drug, thus causing a decrease in drug serum concentration |
| Define distribution. | the process by which the drug becomes available to body fluids and body tissues |
| What factors influence drug distribution? | blood flow, the drug's affinity to the tissue, and the protein-binding effect |
| What are many drugs bound to as they are distributed in the plasma? | protein (primarily albumin) |
| Define highly protein-bound drugs. | drugs that are greater than 89% bound to protein |
| Define moderately highly protein-bound drugs. | drugs that are 61% to 89% bound to protein |
| Define moderatley protein-bound drugs. | drugs that are 30% to 60% bound to protein |
| Define low protein-bound drugs. | drugs that are less than 30% bound to protein |
| Define free drugs. | drugs that are not protein bound |
| Which drugs, protein-bound or free, are active and can cause a pharmacologic response? | free drugs |
| What happens as the free drug in circulation decreases? | more bound drug is released from the protein to maintain the balance of free drug |
| What happens when two highly protein-bound drugs are given together? | they compete for protein-binding sites, thus causing more free drug to be released into the circulation |
| What may be result if two highly protein-bound drugs are given together? | drug accumulation and possible drug toxicity may result |
| How can a low protein level cause a drug overdose? | it decreases the number of protein-binding sites and can cause an increase in the amount of free drug in the plasma |
| How is drug dose prescribed? | according to the percentage in which the drug binds to protein |
| List some causes of low protein levels. | 1. malnutrition2. advanced aging |
| Do all protein-binding drugs cause drug toxicity when a patient has low protein levels? Why or why not? | No, some excess free or unbound drug goes to nonspecific tissue binding sites until needed and excess free drug in the circulation does not occur |
| List the 2 types of proteins that drugs bind to. | 1. albumin2. globulin |
| What protein do most anticonvulsants bind to? | albumin |
| What protein do some basic drugs such as antidysrhythmics (e.g., lidocaine, quinidine) mostly bind to? | globulin |
| What age group is most likely to have hypoalbuminemia? | the elderly |
| What should a nurse do to avoid possible drug toxicity? | 1. checking protein-binding percentage of all drugs admin to client2. check patient's plasma protein and albumin levels |
| What types of lesions/glands hinder drug distribution? | abscesses, exudates, body glands, tumors |
| What sites on the body do antibiotics not distribute well? | abscess and exudate sites |
| What types of tissues do some drugs accumulate at? | fat, bone, liver, muscle, eye tissues |
| Where can drugs be metabolized? | 1. GI tract2. liver |
| What is the primary site of drug metabolism? | the liver |
| What happens to most drugs once they reach the liver? | most are inactivated by liver enzymes and are then converted or transformed by hepatic enzymes to inactive metabolites or water-soluble substances for excretion |
| What does the liver do to lipid-soluble drugs? | the liver metabolizes them into a water-soluble substance for renal excretion |
| What happens if the liver transforms a drug into active metabolites? | it will cause an increased pharmacologic response |
| How do liver diseases such as cirrhosis and hepatitis alter drug metabolism? | by inhibiting the drug-metabolizing enzymes in the liver |
| What happens when the drug metabolism rate is decreased due to liver disease? | excess drug accumulation can occur and lead to toxicity |
| What is the half-life (t 1/2) of a drug? | the time it takes for one half of the drug concentration to be eliminated |
| What 2 processes affect the half-life of a drug? | 1. metabolism2. elimination |
| What happens to the half life a drug with liver or kidney dysfunction? | the half life of the drug is prolonged and less drug is metabolized and eliminated; drug accumulation may occur if the drug is taken continuously |
| How long is a short half-life considered to be? A long half-life? | short= 4-8 hourslong= 24 hours or longer |
| If a drug has a half life of 36 hours, how many times a day would you give the drug? | once a day |
| What is the main metabolizing enzyme in the liver? | cytochrome P450 (85%) |
| How much time does it take for a drug to reach a steady state of serum concentration? | about 5 days |
| Administration of the drug for ________ half lives saturates the biologic system to the extent that the intake of drug equals the amount metabolized and excreted. | 3-5 half lives |
| Digoxin has a half-life of 36 hours. How long would it take to reach a steady state for digoxin concentration? | approx. 5 days to 1 week (3-5 half-lives) |
| What is the main route of drug elimination? | through the kidneys |
| Besides the kidney, what are some other routes of drug elimination? | hepatic metabolism, bile, feces, lungs, saliva, sweat, breast milk |
| What type of drugs do the kidneys filter? | free unbound drugs, water-soluble drugs, and durgs that are unchanged |
| What type of drugs cannot be filtered through the kidneys? | protein-bound drugs |
| What type of drugs do the lungs eliminate? | volatile drug substances and products metabolized to carbon dioxide and water |
| How does urine pH influence drug excretion? | acid urine promotes elimination of weak base drugs and alkaline urine promotes elimination of weak acid drugs |
| Aspirin, a weak acid, is excreted rapidly in alkaline urine. What should be done if a person overdoses on aspirin? | sodium bicarbonate may be given to change the urine pH to alkaline to help potentiate excretion of the drug |
| What would happen if you gave large quantities of cranberry juice to a person who had overdosed on aspirin? | elimination of aspirin would be inhibited because large quantities of cranberry juice can decrease urine pH |
| What type of kidney disease slows or impairs drug excretion and may result in severe adverse drug reactions? | kidney disease that results in decreased glomerular filtration rate (GFR) or decreased renal tubular secretion |
| What is the most accurate test to determine renal function? | creatinine clearance (CLcr) |
| What is creatinine? | a metabolic by-product of muscle that is excreted by the kidneys |
| What factors cause creatinine clearance to vary? | 1. age 2. gender |
| Why are low values of creatinine clearance expected in the elderly and in females? | because of their decreased muscle mass |
| What does a decrease in renal GFR result in? | an increase in serum creatinine level and a decrease in urine creatinine clearance |
| With renal dysfunction either in the elderly or as a result of kidney disorders, should drug doses be increased or decreased? What needs to be determined to establish appropriate drug dosage? | decreased; creatinine clearance should be determined |
| What does the creatinine clearance test consist of? | a 12-24 hour urine collection and a blood sample |
| What are normal creatinine clearance levels? | 85 to 135 ml/min |
| Why does creatinine clearance levels decrease with age? | because aging decreases muscle mass and results in a decrease in functioning nephrons |
| Elderly clients may have a creatinine clearance level of __________. | 60 ml/min |
| Define pharmacodynamics. | the study of drug concentration and its effects on the body |
| ___________ can cause a primary or secondary physiologic effect, or both. | drug response |
| What is the difference between a primary and seocndary physiologic effect caused by a drug response? | a primary effect is desirable, and the secondary effect may be desirable or undesirable |
| Give an example of a drug with a primary and secondary effect. | diphenhydramine (Benadryl): the primary effect is to treat the symptoms of allergy, and the secondary effect is a central nervous system depression that causes drowsiness |
| Define dose response. | the relationship between the minimal versus the maximal amount of drug dose needed to produce the desired drug response |
| All drugs have a ___________ effect. | maximal drug effect (maximal efficacy) |
| Define onset of action. | the tiem it takes to reach the minimum effective concentration (MEC) after a drug is administered |
| Define peak action. | occurs when the drug reaches its highest blood or plasma concentration |
| Define duration of action. | the length of time the drug has a pharmacologic effect |
| What is a time response curve? | a curve that evaluates three parameters of drug action: the onset of drug action, peak action, and duration of action |
| Why is it necessary to understand the time response in relationship to drug administration? | if the drug plasma or serum level decreases below threshold or MEC, adequate drug dosing is not achieved; too high a drug level above the minimum toxic concentration (MTC), can result in toxicity |
| Where are most receptors found? | on cell membranes |
| What are drug-binding sites primarily on? | proteins, glycoproteins, proteolipids, and at enzymes |
| List the 4 receptor families. | kinase-linked receptor; ligand-gated ion channels; G protein-coupled receptor systems; nuclear receptors |
| Define ligand-binding domain. | the site on the receptor in which drugs bind |
| Kinase-linked receptors | the ligand-binding domain for drug binding is on the cell surface. the drug activates the enzyme (inside the cell), and the response is initiated |
| Ligand-gated ion channels | the drug spans the cell membrane and, with this type of receptor, the channel opens, allowing for the flow of ions into and out of the cells; the ions are primarily sodium and calcium |
| G protein-coupled receptor systems | there are 3 components to this receptor response: (1) the receptor, (2) G protein that binds with guanosine triphosphate (GTP), and (3) the effector that is either an enzyme or an ion channel |
| How does the G protein-couple receptor system work? | the drug activates the receptor, which activates G protein, which activates the effect |
| Nuclear receptors | cell nucleus and not on the surface of the cell membrane; activation of receptors through the transcription factors is prolonged; with the first 3 receptor groups, activation of the receptors is rapid |
| How do drugs act through receptors? | by binding to the receptor to produce (initiate) a response or to block (prevent) a response |
| What is the activity of many drugs determined by? | the ability of the drug to bind to a specific receptor; the better the drug fits at the receptor site, the more biologically active the drug is |
| What are agonists? | drugs that produce a response |
| What are antagonists? | drugs that block a response |
| How can the effects of an antagonist be determined? | by the inhibitory (I) action of the drug concentration on the receptor site; IC sub 50 indicates that the drug is effective in inhibiting receptor response in 50% of persons |
| Where are cholinergic receptors located? | bladder, heart, blood vessels, lungs, eyes |
| What are nonspecific drugs? | drugs that affect various sites and have properties of nonspecificity |
| Drugs that evoke a variety of responses throughout the body have a ______________ response. | nonspecific |
| What are nonselective drugs? | drugs that affect various receptors or have properties of nonselectivity |
| How do drugs that produce a response but do not act on a receptor act? | by stimulating or inhibiting enzyme activity or hormone production |
| List the 4 categories of drug action. | (1) stimulation or depression, (2) replacement, (3) inhibition or killing of organisms, and (4) irritation |
| What happens in a drug action that stimulates? | the rate of cell activity or the secretion from a gland increases |
| What happens in a drug action that depresses? | cell activity and function of a specific organ are reduced |
| What types of drugs act by a mechanism of irritation? | laxatives (irritate the inner wall of the colon, thus increasing peristalsis and defecation |
| Drug action may last hours, days, weeks, or months. What does the length of action depend on? | the half-life of the drug; therefore, the half-life is a reasonable guide for the determination of drug dosage |
| What would happen if a drug with a long half-life was given more than once per day? | drug accumulation in the body and drug toxicity are likely to result |
| Define therapeutic index (TI). | estimates the margin of safety of a drug through the use of a ratio that measures the effective (therapeutic or concentration) does (ED) in 50% or persons or animals (ED sub 50) and the lethal dose (LD) in 50% of animals (LD sub 50) |
| low therapeutic index | drugs with a LTI have a narrow margin of safety; drug dosage might need adjustment, and plasma (serum) drug levels need to be monitored because of the small safety range between ED and LD |
| high therapeutic index | drugs with a HTI have a wide margin of safety and less danger of producing toxic effects; plasma (serum) drug levels do NOT need to be monitored routinely for drugs with a high TI |
| The therapeutic range (therapeutic window) of a drug concentration in plasma should be between the _________________________ and ___________________. | the minimum effective concentration in the plasma for obtaining desired drug action and the minimum toxic concentration, the toxic effect |
| What is the peak drug level? | the highest plasma concentration of drug at a specific time |
| What do peak drug levels indicate? | the rate of absorption |
| What is the trough drug level? | the lowest plasma concentration of a drug |
| What does the trough drug level measure? | the rate at which the drug is eliminated |
| When are peak drug levels drawn? | 1-3 hours for oral meds and approx. 10 minutes for IV meds |
| When are trough drug levels drawn? | immediately before the next dose of drug is given, regardless of route of administration |
| When are peak and trough drug levels measured? | when giving drugs that have a narrow therapeutic index and are considered toxic, such as the aminoglycoside antibiotics |
| Define loading dose. | a large initial dose of drug given to achieve a rapid minimum effective concentration in the plasma; after the loading dose is given when immediate drug response is desired, a prescribed dosage per day is ordered |
| What are side effects? | physiologic effects not related to desired drug effects |
| What types of drugs mostly produce side effects? | drugs that lack specificity, such as bethanechol (Urecholine) |
| What is the nurses role in regards to side effects? | the nurse's role includes teaching patients to report any side effects |
| How can some side effects be managed? | with dosing adjustments, changing to a different drug in the same class of drugs, or implementing other interventions |
| What is one of the primary reasons that clients stop taking prescribed medication? | the occurrence of side effects |
| What are adverse reactions? | a range of untoward effects (unintended and occuring at normal doses) of drugs that cause mild to severe side effects, including anaphylaxis (cardiovascular collapse) |
| How can the toxic effects (toxicity) of a drug be identified? | by monitoring the plasma (serum) therapeutic range of the drug |
| What is pharmacogenetics? | the effect of a drug action that varies from a predicted drug response because of genetic factors or hereditary influence |
| What can genetic factors do to a drug? | they can alter the metabolism of the drug in converting its chemical form to an inert metabolite; thus the drug action can be enhanced or diminished |
| Define tolerance. | a decreased responsiveness over the course of therapy |
| Define tachyphylaxis. | a rapid decrease in response to the drug; an "acute tolerance" |
| List the drug categories that can cause tachyphylaxis. | narcotics, barbiturates, laxatives, and psychotropic agents |
| What is a placebo effect? | a psychologic benefit from a compound that may not have the chemical structure of a drug effect |
| The placebo is effective in approx. ______ of persons who take a placebo compound. | 1/3 |
| What are inactive metabolites? | drugs that become inactive after metabolism in the liver |
| What are active metabolites? | when a drug does not change at all by metabolism other than becoming water soluble and is still active (can still produce desired drug effects) until eliminated from the body |
| What is a pro-drug? | a drug converted from inactive to active form in the body during the metabolism process (as well as becoming water soluble) |
| What is a toxic metabolite? | a drug that is converted from a non-toxic drug to a toxic drug during metabolism; e.g., acetominophen (Tylenol) |
| What is the recommended allowance of tylenol (acetominophen) per day? | 4 grams or less per day |
| List the 3 ways in which a drug is eliminated from the kidneys. | (1) glomerular filtration, (2) passive reabsorption, (3) active secretion (transport) |
| What type of drugs can be filtered at the glomerulus? | water soluble, non-bound to protein, and non-ionized drugs |
| What is passive reabsorption? | when drugs are reabsorbed back into the bloodstream from the renal tubule; if the drug still has some fat (lipid soluble) and hasn't been converted all the way to water soluble, it may be reabsorbed |
| What is active secretion (transport)? | secretion by proximal tubule; important for elimination of protein-bound drugs; drugs not filtered through the glomerulus are filtered this way |
| Define affinity. | attraction between a receptor site and a drug |
| What is intrinsic activity? | when the receptor site and drug get together they produce a biologic response in the body |
| Affinity + no intrinsic activity = ??? | antagonist (blockers) |
| What is drug potency? | drugs with higher potency will be needed in smaller doses; takes a smaller dose but you get the same effect as another drug in a higher dose; same class but one is more potent |
| What are the most common mistakes of the 5 rights of medication administration? | (1) wrong dose, (2) wrong drug, (3) wrong route |
Created by:
thehealthynurse
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