Pharmacology Flashcards

Which medication is contraindicated in patients with a history of acute intermittent porphyria?

Answer: Barbiturates

Barbiturates are strongly contraindicated in acute intermittent porphyria because they induce hepatic cytochrome P450 enzymes, specifically ALA synthase, which increases porphyrin precursor production and can precipitate a life-threatening acute attack.

A patient with asthma is prescribed a non-selective beta-blocker for hypertension. What is the expected adverse effect?

Answer: Bronchospasm

Non-selective beta-blockers (e.g., propranolol) block beta-2 receptors in bronchial smooth muscle, causing bronchoconstriction. This can precipitate severe bronchospasm in asthmatic patients. Cardioselective beta-blockers (beta-1 selective) are safer but should still be used cautiously.

A patient on isoniazid for tuberculosis develops peripheral neuropathy. Which vitamin deficiency is responsible and what supplement prevents this?

Answer: Vitamin B6 (pyridoxine)

Isoniazid inhibits pyridoxal phosphokinase and competes with pyridoxal phosphate (active form of vitamin B6), leading to pyridoxine deficiency. This manifests as peripheral neuropathy. Prophylactic pyridoxine (10-25 mg/day) prevents this complication.

Which class of antihypertensive drugs is teratogenic and absolutely contraindicated in pregnancy?

Answer: ACE inhibitors and ARBs

ACE inhibitors and ARBs are teratogenic, particularly in the second and third trimesters, causing renal agenesis, oligohydramnios, pulmonary hypoplasia, and fetal death. They are absolutely contraindicated throughout pregnancy. Methyldopa and labetalol are safe alternatives.

A patient on rifampicin for tuberculosis is also taking warfarin. What effect does rifampicin have on warfarin levels?

Answer: Decreases warfarin levels (inducer)

Rifampicin is one of the most potent inducers of cytochrome P450 enzymes (especially CYP3A4, CYP2C9). It accelerates warfarin metabolism, significantly decreasing warfarin levels and anticoagulant effect, requiring substantial dose increases and close INR monitoring.

Which antidiabetic medication works by inhibiting sodium-glucose cotransporter 2 (SGLT2) in the proximal tubule?

Answer: Empagliflozin

Empagliflozin (and other gliflozins: dapagliflozin, canagliflozin) inhibits SGLT2 in the proximal renal tubule, reducing glucose reabsorption and causing glycosuria. These drugs also have cardiovascular and renal protective benefits independent of glucose lowering.