Undergraduate Pharmacology: Drug Interactions - Vocabulary Flashcards

Vocabulary flashcards covering key terms and concepts from the Drug Interactions lecture notes.

Drug interaction

Pharmacological or clinical response to a drug combination that differs from the expected effects of the two drugs given alone; includes antagonism and synergism.

Antagonism

A drug interaction where the combined effect is less than the sum of the effects of each drug given alone.

Synergism

A drug interaction where the combined effect is greater than the sum of the individual effects.

Pharmacokinetic interaction

An interaction in which one drug changes the absorption, distribution, metabolism, or excretion of another, altering its plasma concentration.

Pharmacodynamic interaction

An interaction where one drug changes a patient’s response to another drug without changing the kinetics of the second drug.

Pharmaceutical interaction

Physical or chemical incompatibilities between drugs (e.g., IV admixtures).

Drug-food interaction

Interactions between drugs and foods or other non-drug substances (enteral products, nutrients, alcohol, tobacco) affecting absorption or effect.

Enteral products

Foods or nutrients administered through the GI tract that can interact with drugs.

Narrow therapeutic range

Drugs with a small margin between therapeutic and toxic doses (e.g., digoxin, theophylline).

Steep dose–response curve

Small changes in dose produce large changes in effect (e.g., phenytoin, aminoglycosides).

Object drugs

Drugs with a narrow therapeutic range, a steep dose–response, hepatic metabolism, and typically used chronically.

Complexation

Mechanism where two drugs form a chemical complex, reducing absorption (e.g., with cholestyramine or metal ions in antacids).

Bile acid resins

Cholestyramine and colestipol; form complexes that lower absorption of other drugs.

Metal ions in interfering products

Divalent/trivalent ions (Mg2+, Ca2+, Zn2+, Fe2+/Fe3+, Al3+) in antacids/multivitamins that chelate drugs and reduce absorption.

Changes in pH (absorption)

Drug-induced pH changes that alter dissolution and absorption; examples include H2 blockers, PPIs, and antacids.

H2 receptor blockers

Cimetidine and ranitidine; raise gastric pH and can reduce absorption of acid-dependent drugs.

Proton pump inhibitors

Omeprazole and lansoprazole; raise gastric pH, affecting dissolution of some drugs.

Antacids

Alkaline preparations that raise gastric pH and can affect dissolution of certain drugs.

Drugs needing acid pH for dissolution

Drugs that require acidic conditions to dissolve (e.g., ketoconazole, itraconazole, iron supplements).

Changes in GI motility

Drugs that slow (e.g., opioids, anticholinergics; antihistamines, TCAs, phenothiazines) or speed (e.g., laxatives, metoclopramide, erythromycin) GI transit, altering absorption.

Opioids (GI effect)

Drugs that slow GI motility, potentially delaying absorption.

Erythromycin (GI effect)

A macrolide that can speed GI motility, altering absorption of concomitant drugs.

Absorption (drug interactions)

Pharmacokinetic interactions that change the extent or rate of drug absorption.

Cytochrome P‑450 (CYP450)

A family of enzymes responsible for drug metabolism; major isoforms include CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP3A4/3A3.

CYP2D6 polymorphism

Genetic variation leading to poor, intermediate, extensive, or ultrarapid metabolism; ~25% of clinically used drugs metabolized by CYP2D6.

Poor metabolizer

Individual with very low CYP2D6 activity, leading to slower drug metabolism.

Ultrarapid metabolizer

Individual with high CYP2D6 activity, leading to faster drug metabolism.

Factors affecting metabolism: age (very young)

In neonates, glucuronidation is immature (Gray Baby syndrome) due to deficient Phase-2 enzymes.

Factors affecting metabolism: elderly

Reduced metabolism and excretion; more drugs used concurrently; dosing escalation often needed.

Disease state effect on metabolism

Liver diseases (hepatitis, hepatic cancer) reduce drug clearance and increase overdose risk.

Enzyme induction

Drugs that increase hepatic metabolic enzyme levels, increasing metabolism of substrates; onset days to weeks; offset weeks after stopping.

Enzyme inducers

Examples include barbiturates, phenytoin, primidone, carbamazepine, rifampin, ritonavir, plus cigarette smoking, chronic alcohol use, charbroiled meat.

Time course of induction

Induction onset ~5 days; maximum ~2 weeks; offset 3+ weeks after stopping.

Enzyme inhibition

Drugs that decrease CYP enzyme activity, increasing substrate concentrations and effects.

Time course of inhibition

Inhibition often rapid; maximal within 24 hours; offset usually within 24 hours after discontinuation.

Important enzyme inhibitors

Amiodarone, cimetidine, ciprofloxacin, clarithromycin, diltiazem, fluoxetine, ketoconazole, lovastatin, metoclopramide, omeprazole, SMX/TMP, sertraline, verapamil, ticlopidine.

Pharmacodynamic interaction

Effect of one drug on the concentration–effect relationship of another drug without pharmacokinetic changes.

Antagonistic pharmacodynamic interactions

One drug reduces or blocks the effect of another (example: cholinergic antagonist diminishing cholinergic therapy).

Synergistic/additive pharmacodynamic effects

Combined effects that are greater (or more adverse) than either drug alone.

Additive CNS depressant effects

Combined sedation from alcohol, analgesics, antihistamines, barbiturates, benzodiazepines, beta-blockers, anticonvulsants, sedatives, phenothiazines, TCAs, anesthetics, muscle relaxants.

Additive anticholinergic effects

Cumulative antimuscarinic effects from multiple drugs (e.g., haloperidol, amitriptyline, benztropine, scopolamine, dicyclomine, diphenhydramine, benzodiazepines).

Antagonistic example

Cholinergic and anticholinergic drugs (e.g., donepezil with tolterodine) may worsen urinary incontinence through opposing actions.

Herbs and drug interactions: Ginseng

Ginseng can increase INR when taken with warfarin.

Herbs and drug interactions: Garlic

Garlic has antiplatelet effects; interactions with aspirin, warfarin, ticlopidine, clopidogrel, dipyridamole.

Herbs and drug interactions: Ginkgo biloba

Ginkgo has antiplatelet effects; interactions with aspirin, warfarin, ticlopidine, clopidogrel, dipyridamole.

Herbs and drug interactions: Ginger

Ginger can potentiate anticoagulants (e.g., warfarin) via thromboxane pathway effects.

Herbs and drug interactions: St. John’s Wort

Herbal that can induce CYP enzymes and affect MAOI/SSRI interactions; can reduce levels of many drugs.