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Pharm Ch 7

Drug Interactions and OTC Drugs

What type of clients are at most risk for having a drug interaction? those who have chronic health conditions, take multiple medications, see more than one HCP, and use multiple pharmacies, also older adults (75% take prescription drugs and 82% take OTC preparations)
Define drug interaction. an altered or modified action or effect of a drug as a result of interaction with one or more other drugs
Define adverse drug reaction. an undesirable drug effect that ranges from mild untoward effects to severe toxic effects, including hypersensitivity reaction and anaphylaxis
Define drug incompatibility. a chemical or physical reaction that occurs among two or more drugs in vitro; in other words, the reaction occurs between two or more drugs within a syringe, IV bag, or any other artificial environment outside the body
What 2 categories are drug interactions divided into? (1) pharmacokinetic reactions; (2) pharmacodynamic reactions
What are pharmacokinetic interactions? changes that occur in the absorption, distribution, metabolism or biotransformation, and excretion of one or more drugs
What can happen if a person takes two drugs at the same time? the rate of absorption of one or both drugs can change; one drug can block, decrease, or increase the absorption rate of another drug
How can a drug block, decrease, or increase the absorption rate of another drug? (1) by decreasing or increasing gastric emptying time; (2) by changing the gastric pH; and (3) by forming drug complexes
What type of drugs increase the speed of gastric emptying? How may these drugs affect drug absorption? laxatives or metoclopramide; lead to an increase in gastric and intestinal motility and cause a decrease in drug absorption
Where are most drugs absorbed? the small intestine
What drugs are not absorbed in the small intestine? barbiturates, salicylates, and theophylline
What do narcotics and anticholinergic drugs (e.g., atropine) do to absorption rate? increase absorption rate by decreasing gastric emptying time and GI motility
For drugs that undergo gastric absorption, does the amount/extent of absorption increase or decrease the longer the drug remains in the stomach? increases
Are weakly acidic drugs (e.g., aspirin) absorbed slower or faster in decreased gastric pH? more rapidly absorbed and less ionized
Drugs that ______ the pH of gastric juices _____________ absorption of _______ -acid drugs. increase, decrease, weak-acid
How do antacids such as Maalox and Amphojel affect gastric pH and absorption? they raise gastric pH and block/slow absorption
What products should be avoided 1 hour before and 2 hours after tetracycline or ciprofloxacin consumption? dairy products, multivitamins, and antacids
What drugs can form complexes with other drugs prevent their absorption (due to being less soluble)? antacids, certain cholesterol-lowering drugs such as cholestyramine and colestipol
What type of situations would drug complexation be desired? activated charchoal administered after a toxic ingestion of a medication to decrease its absorption and, consequently, any untoward effects associated with the overdose
Give an example of how the alteration of bacteria normally found in the GI tract may impact the pharmacokinetics of a medication. intestinal microflora can digest digoxin; microflora metabolize digoxin which decreases its bioavailability; if patient is given antibiotic that destroys/inhibits these organisms, there will be an increase in the absorption of digoxin
antibiotics and oral contraceptives gut bacteria hydrolyze estrogen conjugates to free estrogen so they may be absorbed and exert their effect; concurrent antibotic admin. may alter intestinal bacteria thereby impairing this process and decrease contraceptive absorption/effectiveness
What may affect a drug's distribution to tissues? its binding to plasma/serum protein
What drugs are free active agents and can enter body tissues? unbound drugs
What may result if two highly protein bound drugs are administered simultaneously? drug displacement
List the factors that influence drug displacement. (1) the drug concentration in the blood; (2) protein-binding power of the drugs; (3) volume of distribution (Vd)
Two drugs that are highly protein bound will compete for binding sites in the plasma. What will result? a decrease in protein binding of one or both drugs; therefore, more free drug circulates in the plasma and is available for drug action; this can lead to drug toxication
What usually happens if two highly protein bound drugs need to be taken concurrently? the drug dosage of one or both drugs may need to be decreased to avoid drug toxicity
Give some examples of drugs that are highly protein bound. the anticoagulant warfarin, anticonvulsants such as phenytoin and valproic acid, gemfibrozil, most NSAIDS, sulfisoxazole, glyburide, and quinidine
What percentage of Warfarin is protein bound? 99%, allowing only 1% to be free drug
Liver disease/poor nutritional status & protein-bound drugs a significant decrease in the serum albumin level because of liver disease or poor nutritional status can increase the free drug amt. of highly protein bound drugs making more drugs available to exert its pharmacological effect
Many drug interactions of metabolism occur with the induction or inhibition of the ____________________. hepatic microsomal system
How can a drug increase the metabolism of another drug? by stimulating liver enzymes
What are drugs that promote induction of enzymes called? enzyme inducers
Give an example of an enzyme inducer. barbiturates such as phenobarbital
What drugs does phenobarbital increase the metabolism of? most antipsychotics and theophylline
What does an increase in metabolism result in? promotion of drug elimination and decreases in plasma concentration of the drug; the result is a decrease in drug action; drug metabolites may be excreted or may produce an active pharmacologic response
The anticonvulsant drugs phenytoin and carbamazepine and the antimicrobial medication rifampin are hepatic enzyme reducers that can __________________ drug metabolism, for example, for the anticoagulant drug Warfarin. increase
What should be done if a patient is concurrently taking warfarin and a hepatic inducer? Why? a larger dose of warfarin is usually needed because metabolism aids in decreasing the amount of the drug
How long does it take for an enzyme inducer drug to interact with another drug? How long does it last usually interaction occurs after 1 week of drug therapy and can continue for 1 week after the drug inducer is discontinued
Cigarette smoking ___________ hepatic enzyme activity and can _______________ theophylline clearance. increase; increase
With chronic alcohol use, hepatic enzyme activities are ______________; with acute alcohol use, metabolism is ____________. increase; inhibited
Some drugs are also enzyme inhibitors. Give an example. antiulcer drug cimetidine; decreases metabolism of certain drugs such as theophylline; as a result there is an increase in plasma conc. of theophylline
What should be done if a person on theophylline is given an enzyme inhbitor such as cimetidine? the dose of theophylline should be decreased to avoid toxicity
Besides cimetidine, what are some other enzyme inhibitors? erythromycin and itraconazole, an antifungal medication
What particles found in cigarette smoke induce production of the specific family of enzymes responsible for theophylline metabolism? polycyclic aromatic hydrocarbons
What does chronic cigarette smoking lead to? an increase in hepatic enzyme activity and can increase theophylline clearance
What should be done if asthmatics who smoke take theophylline to manage their disease? may require an increase in theophylline dosage
What happens to hepatic enzyme activities with chronic alcohol use? Acute alcohol use? they are increased; metabolism is inhibited
What natural or herbal products induces the metabolism of certain drugs such as warfarin, digoxin, and theophylline? What does this action do? St. Johns Wort, and OTC herbal product to manage symptoms of depression; this action potentially decreases the effectiveness of these medications, possibly necessitating a dose increase to sustain efficacy
Clients who are stablized on therapeutic doses of carbamazepine, diazepam, or a statin need to stay away from what products? Why? stay away from grapefruit products because they may subject themselves to adverse effects from greater-than-expected drug levels if they eat or drink grapefruit products concurrently with the drug
Why shouldn't grapefruit products be taken with certain drugs? because the flavonoids, a group of naturally occurring compounds found in the juice and pulp of citrus fruits, are potent inhibitors of the metabolism of certain drugs
What do certain drugs that alter hepatic blood flow cause? a decrease in liver metabolism
Where are most drugs filtered? through the glomeruli
Besides urine, where does excretion of some drugs occur? in bile, which passes into the intestinal tract
What type of drugs can decrease or delay drug excretion? drugs that decrease cardiac output, decrease blood flow to the kidneys, and decrease glomerular filtration
What drug does the antiarrhythmic drug quinidine decrease the excretion of? What can occur because of this? digoxin; therefore, plasma conc. of digoxin is increased and digitalis toxicity can occur
What do diuretics do? promote water and sodium excretion from the renal tubules
What diuretic acts on the loop of Henle? Furosemide (Lasix)
What diuretic acts on the distal tubules? hydrochlorothiazide (HydroDIURIL)
What do Lasix and HydroDIURIL decrease the reabsorption of? water, sodium, and potassium
A renal loss of potassium, which may lead to a condition known as ____________________, can __________ the action of digoxin and digitalis toxicity could occur. hypokalemia; enhance
What happens when two or more drugs undergo the same route of excretion? they may compete with one another for elimination from the body
How does Probenecid (Benemid), a drug for gout, decrease penicillin excretion? by inhibiting the secretion of penicillin in the renal tubules of the kidneys; in some cases this effect may be desirable to increase or maintain the plasma conc. of penicillin (has short half-life) for a prolonged period of time
Changing urine pH affects drug excretion. The antacid sodium bicarbonate causes the urine to be alkaline. What does alkaline urine promote? the excretion of drugs that are weak acids (e.g., aspirin and barbiturates); also promotes reabsorption of weak base drugs
What does acid urine promote the excretion of? drugs such as quinidine that are weak bases
Define therapeutic drug monitoring. checking serum drug levels
Give examples of drugs that require therapeutic drug monitoring. digoxin and phenytoin
What are pharmacodynamic interactions? those that result in additive, synergistic or antagonistic drug effects
Define additive effect. the drug interaction that results when two drugs with similar action are administered; the sum of the effects of two drugs
Give an example of a desirable additive effect. when a beta blocker and a diuretic are administered for treatment of hypertension; used in combination, these two drugs utilize diff. mechanisms to have a more pronounced BP lowering effect
Give an example of an undesirable additive effect. 2 vasodilators: hydralazine (Apresoline) prescribed for HTN and nitroglycerin prescribed for angina; the result could be severe hypotensive response
Define synergistic effect. when 2 or more drugs are given together, one drug can potentiate the other; the clinical effect is substantially greater than the combined effect of the two
Give an example of a synergistic effect. combination of meperidine (Demerol, narcotic analgesic) and promethazine (Phenergen, antihistamine); major side effect of prom. is sedation; when used with mep. in post-surg. clients the prom. enhances drowsiness effect of meperidine; less mep. is req.
Give an example of an undesirable synergistic effect. when alcohol and a sedative-hypnotic drug such as chlordiazepoxide (Librium) or diazepam (Valium) are combined; CNS depression increases as a result
Some antibacterials (antibiotics) have an enzyme inhibitor added to the drug to potentiate the therapeutic effect. Give some examples. ampicillin with sulbactam and amoxicillin with clavulanate, in which sulbactam and clavulanate potassium are bacterial enzyme inhibitors
What happens if ampicillin and amoxicillin are given without bacterial enzyme inhibitors? the desired therapeutic effect may not occur because of the bacterial beta-lactamase which inactivates the drugs and causes bacterial resistance
What are antagonistic effects? two drugs in opposing drug categories cancel drug effects of both drugs
Give an example of an antagonistic effect? when the adrenergic beta stimulant isoproterenol (Isuprel) and the adrenergic beta blocker propranolol (Inderal) are given together.
Why shouldn't isoproterenol and propranolol be given together? Isoproterenol is a drug used in emergency situations to treat bradycardia (HR<60bpm); if given to a client receiving a drug that increases BP and HR, the action of each drug is cancelled; neither delivers the expected therapeutic effect
Give an example of a situation in which the antagonistic effect is desirable. in the case of morphine overdose, naloxone is given as an antagonist (antidote) to block the narcotic response
The use of two prescription drugs can have additive, synergistic, antagonistic, or no effect. Give an example. warfarin; when taken with another drug, the effects of the second drug can increase, decrease, or have no effect on the anticoagulant
List some common symptoms of drug-drug interactions. nausea, GI upset, headache, and dizziness
What can food do to drug absorption? it can increase, decrease, or delay drug absorption
Food can bind with drugs, causing less or slower drug absorption. Give an example. the interaction of tetracycline and dairy products; the result is a decrease in the plasma conc. of tetracycline; because of binding effect, tetracycline should be taken 1 hour before or 2 hours after meals and should not be taken with dairy products
Why shouldn't you take levothyroxine (used to treat hypothyroidism) with food? because food makes the absorption of this drug erratic
Food may also have an impact on the absorption of different dosage forms of the same drug. Give an example. Itraconazole solution is best absorbed on an empty stomach; the capsules require an acidic env. have a higher availability when given with food
List some drugs in which food increases drug absorption. the antibiotic introfurantoin (Macrodantin), the beta blocker metoprolol (Lopressor), and the cholesterol-lowering lovastatin (Mevacor)
The composition of a meal may also influence drug absorption. Give an example. the absorption of levodopa, one component of the antiparkinsonism drug Sinemet, is sig. reduced when taken with high protein meals
When does the classic drug-food interaction occur? when an antidepressant of the monoamine oxidase (MAO) inhibitor type (e.g., phenelzine) is taken with tyramine-rich foods; more norepinephrine is released, and the result could be a hypertensive crisis
What foods should be avoided when taking monoamine oxidase inhibitors? tyramine-rich foods such as cheese, wine, organ meats, beer, yogurt, sour cream, or bananas
Abnormal plasma or serum electrolyte concentrations can affect certain drug therapies. Give an example. if a client takes digoxin and has decreased serum K and serum Mg levels or increased serum Ca levels, digitalis toxicity may result
Certain drugs, such as those from the thiazide diuretic group, can cause abnormal electrolyte levels. Give an example. hydrocholorthiazide (HydroDIURIL), which can decrease serum K, Mg, and Na levels and can increase serum Ca levles; promotes K loss, and low serum K results in inc. in uptake of digoxin by myocardial tissue
What should the nurse observe in a client taking digoxin and hydrochlorothiazide? Why? observe client for digitalis toxicity; sensitization of the myocardium to digoxin becuase of the hydrochlorothiazide increases risk of digitalis-induced arrhythmias
List the symptoms of digitalis toxicity. nausea, vomiting, bradycardia, and stated visual problems
What is a drug-induced photosensitivity reaction? a skin reaction that is caused by exposure to sunlight
What causes a photosensivity reaction? the interaction of a drug and exposure to UVA light, which can cause cellular damage; usually the skin area that is exposed is affected
What are the 2 types of photosensitivity reactions? photoallergy and phototoxicity
When does a photoallergy occur? when a drug (e.g., sulfonamide) undergoes activation in the skin by UV light to a compound that is more allergenic than the parent compound; because it takes time to develop antibodies, this rxn is a type of delayed hypersensitivity reaction
When does phototoxicity occur? when a photosensitive drug undergoes photochemical reactions within the skin to cause damage; onset with erythema can be rapid, occurring within 2-6 hrs of sunlight exposure
How is phototoxicity different from a photoallergy? it is not immune-mediated
How are both types of photosensitivity reactions alike? Different? both are result of light exposure; phototoxicity may result of the drug dose, whereas photoallergenic rxns are not and only require previous exposure, or sensitization, to offending agent
How can most photosensitive reactions be avoided? by using sunscreen with a protective factor (SPF) greater than 15, avoiding excessive sunlight, and wearing protective clothing
What are over-the-counter drugs? drugs that can be obtained without a prescription
Durham-Humphrey amendment (in 1952) to the Food, Drug, and Cosmetic Act of 1938 allowed FDA drugs considered safe for consumption to be sold as nonprescription or OTC drugs
What did the 1962 Kefauver-Harris amendment require? required proof of efficacy and safety of drugs; the catalyst for this amendment was the # of thalidomide-induced birth defects found in Europe during the 1950s
What 3 categories does the FDA place drugs? Category I: drugs judged to be both safe and effective; Category II: drugs judged to be either unsafe or ineffective--not included in OTC products; Category III: drugs for which there are insufficient data to judge safety or efficacy
List some cautions that may be of assistance when OTC preparations are considered. pp. 145-146
What OTC drugs should patient taking maintenance medications for a cough/cold avoid? OTC cough medicines because of potential for drug-drug interaction
What OTC drugs should a patient with ashtma avoid? aspirin because it can trigger an acute asthma episode
When is aspirin not recommended for children? flu symptoms or chickenpox, because it has been associated with Reye syndrome
What OTC drugs should patients with impaired renal function avoid? aspirin, acetaminophen, and ibuprofen because each can further decrease renal function, esp. with long-term use
What are clients taking moderate to high doses of aspirin, ibuprofen, or naproxen concurrently with an anticoagulant, at an increased risk for? bleeding
List some ingredients that most OTC cough and cold remedies contain. guaifenesin, dextromethorphan, pseudoephedrine, an analgesic, and an antihistamine
The majority of ingredients used to treat nasal congestion are sympatheomimetic. What does this mean? they stimulate the sympathetic nervous system
Give some examples of sympatheomimetic drugs. phenylephrine, phenylpropanolamine, and pseudoephedrine
Why did the FDA order removal of phenylpropanolamine from OTC cold remedies and weight-control drugs? because of the increased risk of hemorrhagic stroke in young women who take the drug; it has been reported that this drug may also cause psychosis, HTN, renal failure, and cardiac dysrhythmias
OTC cough and cold remedies are primarily safe for children older than _______ years. six
What medical conditions should not take OTC drugs without first approval from HCP? heart disease, HTN, or thyroid disease
List the side effects of cough and cold OTC drugs that contain a sympathomimetic. headache, nervousness, increase BP, and insomnia
What is the most common side effect of an antihistamine? drowsiness
Give an example of an iatrogenic condition. when a person medicated with antiinflammatory steroids develops a Cushing's appearance
Sleep aids should not be taken with a depressant. Why? because they can have an additive depressive effect on the CNS
What are side effects of amphetamines (used to be taken as weight loss drug; suppressed appetite)? nervousness, heart palpitations, increased BP, and insomnia
For what patients are weight-control drugs contraindicated in? patients with heart disease, HTN, DM, and thyroid disease
What was the first FDA-approved OTC weight loss medication sold in the US without a prescription (2007)? orlistat-OTC (Alli)
How does orlistat-OTC (Alli) work? by inhibiting lipase enzymes within the GI tract; blocks dietary absorption of fat by about 30%
What are the most common side effects of orlistat-OTC (Alli)? oily spotting in underwear, flatulence, urgent bowel movements, and fatty or oily stools
Created by: thehealthynurse
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