Cardiac Pharmacology and Therapeutics
Items test mechanism, contraindication, and clinically important interaction rather than simple drug lists; expect questions that embed a second drug or a comorbidity to change the answer.
Core agents
- Beta-blockers: cardioselective agents are safer in bronchospasm; intrinsic sympathomimetic activity is undesirable after infarction; avoid in cocaine toxicity and decompensated heart failure.
- ACE inhibitors and ARBs: cough with ACE inhibitors, angioedema, hyperkalaemia, and acute kidney injury; contraindicated in pregnancy and bilateral renal artery stenosis.
- Calcium channel blockers: dihydropyridines cause peripheral oedema; verapamil and diltiazem are negative inotropes and are avoided in HFrEF.
- Amiodarone: long half-life, thyroid, pulmonary, hepatic, ocular, and neurological toxicity; raises warfarin and digoxin levels.
- Digoxin: narrow therapeutic index; toxicity is potentiated by hypokalaemia, hypomagnesaemia, and renal failure; treat with digoxin-specific antibody fragments.
- Anticoagulants: DOACs preferred in non-valvular AF; idarucizumab reverses dabigatran and andexanet reverses factor Xa inhibitors.
Antiplatelet pharmacogenetics
- Clopidogrel is a prodrug requiring CYP2C19; poor metabolisers have reduced benefit, which is why ticagrelor is preferred after ACS.
Worked example
A patient stable on warfarin for a mechanical mitral valve starts amiodarone. Amiodarone inhibits CYP2C9 and P-glycoprotein, so the warfarin dose is reduced (commonly by one-third to one-half) with INR checks twice weekly for 2 weeks, and the digoxin dose is likewise reviewed.
Traps
- Adenosine has a half-life of seconds; give by rapid bolus with immediate flush.
- Nitroprusside can cause cyanide toxicity in renal failure or prolonged high-dose use.
- Statin interactions with macrolides and azoles raise the risk of rhabdomyolysis.