Pharmacology Principles Flashcards

In elderly patients, which pharmacokinetic change is most clinically important when prescribing drugs that are renally eliminated?

Answer: Reduced renal clearance prolonging drug half-life

Renal function declines with age (GFR decreases ~1 mL/min/year after 40), prolonging the half-life of renally cleared drugs and increasing accumulation risk at standard doses.

Neonates are at risk of 'grey baby syndrome' from chloramphenicol due to which pharmacokinetic limitation?

Answer: Reduced glucuronidation capacity in the immature liver

Neonates have immature hepatic UDP-glucuronosyltransferase (UGT) enzymes, impairing glucuronidation of chloramphenicol, leading to toxic accumulation and cardiovascular collapse.

In severe hepatic impairment (Child-Pugh C), which drugs require the greatest dosing caution?

Answer: Drugs with a high hepatic extraction ratio

High hepatic extraction ratio drugs (e.g., morphine, propranolol) rely heavily on liver blood flow and enzyme activity; hepatic impairment severely reduces their first-pass and systemic clearance.

Therapeutic drug monitoring (TDM) is most clinically valuable for drugs with which characteristic?

Answer: Narrow therapeutic index where small concentration changes cause toxicity or failure

TDM is indicated for drugs with narrow therapeutic indices (e.g., digoxin, lithium, gentamicin, phenytoin) where sub-therapeutic or toxic concentrations produce significant clinical consequences.

A drug exhibits zero-order kinetics at high plasma concentrations. Which statement best describes zero-order elimination?

Answer: A constant amount of drug is eliminated per unit time, independent of concentration

Zero-order kinetics occurs when elimination pathways are saturated; a fixed amount (not fraction) of drug is eliminated per unit time, so half-life lengthens as concentration rises.

A pregnant patient requires an antibiotic. Which class is avoided due to risk of dental discolouration and inhibited bone development in the fetus?

Answer: Tetracyclines

Tetracyclines cross the placenta and chelate calcium in developing fetal bones and teeth, causing permanent yellow-brown dental staining and impaired skeletal development.

A patient on warfarin (target INR 2.0-3.0 for atrial fibrillation) has an INR of 6.5 with no active bleeding. According to standard prescribing guidance, the most appropriate immediate action is:

Answer: Stop warfarin temporarily and consider low-dose oral vitamin K

For INR 5.0-8.0 with no bleeding, guidelines recommend withholding warfarin and giving low-dose oral vitamin K (1-2 mg) with close INR follow-up.