Pharmacology Basics Flashcards

How is the therapeutic index of a drug calculated?

Answer: TD50 divided by ED50

The therapeutic index is the toxic dose divided by the effective dose; a low ratio means a narrow safety margin.

Which substance is eliminated by zero-order kinetics at typical concentrations?

Answer: Ethanol

Alcohol dehydrogenase saturates, so a fixed amount of ethanol is removed per hour.

Volume of distribution (Vd) is best defined as:

Answer: The apparent volume needed to hold the total body drug amount at the plasma concentration

Vd is a theoretical volume equal to the dose divided by plasma concentration.

Which prodrug needs activation by CYP2C19, so poor metabolizers get less benefit from it?

Answer: Clopidogrel

Clopidogrel is converted to its active antiplatelet metabolite mainly by CYP2C19.

A patient on theophylline develops toxicity after starting an antibiotic. Which antibiotic most likely raised the theophylline level?

Answer: Ciprofloxacin

Ciprofloxacin inhibits CYP1A2, which slows theophylline clearance.

Why can gel separator tubes cause falsely low results for some drugs?

Answer: The gel absorbs some lipophilic drugs

Lipophilic drugs such as some tricyclic antidepressants can move into the gel barrier during storage.

What is the bioavailability of a drug given intravenously?

Answer: 100%

IV drugs go directly into the circulation, so none is lost to absorption or first-pass metabolism.