Editing Pharmacology – RN Flashcards (section)

== Pharmacokinetics and Principles ==

;What is the first-pass effect and why does it matter clinically?
:Oral drugs absorbed from the gut pass through the portal circulation and are metabolized by the liver before reaching systemic circulation. It explains why oral doses are larger than intravenous doses of the same drug, and why sublingual, transdermal, rectal, and parenteral routes bypass hepatic metabolism and yield higher bioavailability.

;How many half-lives are needed to reach steady state, and why does that matter?
:About four to five half-lives on a fixed dosing schedule. It explains delayed therapeutic effect, the use of loading doses when rapid effect is needed, and the time required for a drug to clear after discontinuation.

;Why does hypoalbuminemia increase the risk of drug toxicity?
:Only the unbound (free) drug fraction is pharmacologically active. With low albumin, a larger free fraction circulates, so highly protein bound drugs such as warfarin and phenytoin produce exaggerated effects at ordinary doses.

;Name common cytochrome P450 inducers and inhibitors and their effect on serum drug levels.
:Inducers such as rifampin, phenytoin, carbamazepine, phenobarbital, and St. John's wort increase metabolism and lower levels of other drugs. Inhibitors such as azole antifungals, erythromycin and clarithromycin, and grapefruit juice decrease metabolism and raise levels, increasing toxicity risk.

;Define narrow therapeutic index, list classic examples, and state when a trough is drawn.
:A small difference between the therapeutic and toxic dose, requiring serum level monitoring. Examples: digoxin, lithium, phenytoin, theophylline, warfarin, vancomycin, and aminoglycosides. The trough is drawn immediately before the next scheduled dose; the peak, drawn after administration at a drug-specific interval, reflects toxicity risk.