Pharmacology Flashcards

A patient with epilepsy on carbamazepine develops Stevens-Johnson syndrome. Which HLA allele is associated with increased risk?

Answer: HLA-B*15:02

HLA-B*15:02 is strongly associated with carbamazepine-induced Stevens-Johnson syndrome and toxic epidermal necrolysis, particularly in Southeast Asian populations. SCFHS guidelines recommend HLA testing before starting carbamazepine in at-risk populations.

A patient on heparin develops heparin-induced thrombocytopenia (HIT) type II. What is the most appropriate alternative anticoagulant?

Answer: Argatroban (direct thrombin inhibitor)

In HIT type II, all heparins (including LMWH due to cross-reactivity) must be stopped. A non-heparin anticoagulant such as argatroban (direct thrombin inhibitor) or fondaparinux should be initiated. Warfarin alone is contraindicated acutely as it can cause skin necrosis.

Which drug is used as a first-line disease-modifying antirheumatic drug (DMARD) for rheumatoid arthritis?

Answer: Methotrexate

Methotrexate is the anchor DMARD and first-line treatment for rheumatoid arthritis. It works by inhibiting dihydrofolate reductase and has immunomodulatory effects. It is given weekly (not daily) with folic acid supplementation. Monitoring includes FBC, LFTs, and renal function.

A child is accidentally given a large dose of iron supplement. What is the specific antidote?

Answer: Desferrioxamine (deferoxamine)

Desferrioxamine (deferoxamine) is the specific chelating agent for iron poisoning. It binds free iron to form ferrioxamine, which is excreted renally (causing vin rosé coloured urine). It is indicated when serum iron exceeds 500 μg/dL or there are systemic symptoms.

A patient with gout is prescribed allopurinol. What is its mechanism of action?

Answer: Inhibits xanthine oxidase

Allopurinol is a xanthine oxidase inhibitor that blocks the conversion of hypoxanthine to xanthine and xanthine to uric acid, thereby reducing uric acid production. It should not be started during an acute gout attack as it can worsen the flare.

Which of the following medications requires therapeutic drug monitoring due to its narrow therapeutic index in bipolar disorder treatment?

Answer: Lithium

Lithium has a narrow therapeutic index (0.6-1.0 mEq/L for maintenance, 1.0-1.2 for acute mania). Regular monitoring of serum lithium levels, renal function, thyroid function, and calcium is mandatory. Toxicity occurs at levels >1.5 mEq/L and can be life-threatening.