Pharmacokinetics and Drug Metabolism Flashcards
7 cards from real Pharmacology practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Pharmacokinetics and Drug Metabolism flashcards as text
A drug with a high extraction ratio is administered orally. Which phenomenon most significantly reduces its systemic bioavailability?
Answer: First-pass metabolism
High-extraction-ratio drugs are extensively metabolized by the liver on first pass, greatly reducing the fraction that reaches systemic circulation.
Which cytochrome P450 isoform is responsible for metabolizing approximately 50% of all clinically used drugs?
Answer: CYP3A4
CYP3A4 is the most abundant hepatic CYP enzyme and metabolizes roughly half of all drugs in clinical use.
A patient taking rifampin begins a new medication. The new drug's plasma levels are unexpectedly low. What is the most likely explanation?
Answer: Rifampin induces CYP450 enzymes
Rifampin is a potent CYP450 inducer that increases metabolism of co-administered drugs, lowering their plasma concentrations.
What is the clinical significance of a drug having a large volume of distribution (Vd)?
Answer: The drug distributes extensively into tissues
A large Vd indicates that the drug distributes widely into peripheral tissues rather than remaining in the plasma compartment.
Which phase II metabolic reaction conjugates drugs with glucuronic acid?
Answer: Glucuronidation
Glucuronidation, catalyzed by UDP-glucuronosyltransferases, is the most common phase II conjugation reaction that enhances water solubility.
A drug's half-life is 6 hours. How long does it take to reach approximately 94% of steady-state concentration during continuous infusion?
Answer: 24 hours
Steady state is reached after approximately 4-5 half-lives; 4 half-lives (4 × 6 = 24 hours) yields about 94% of steady state.
Which type of pharmacokinetics applies when drug-metabolizing enzymes become saturated, causing a disproportionate increase in plasma concentration with increasing dose?
Answer: Zero-order kinetics
Zero-order (capacity-limited) kinetics occur when enzyme saturation causes a constant amount of drug to be eliminated per unit time regardless of concentration.