Cardiovascular pharmacology questions.

Answer: It blocks β₂ receptors in bronchial smooth muscle

Propranolol is non-selective, so it blocks β₂ as well as β₁. β₁ blockade is the effect you wanted in the heart; β₂ blockade is the same drug acting on bronchial smooth muscle, where it opposes bronchodilation. One mechanism, two organs, and the second organ is why cardioselective agents exist.

Answer: Prevent the breakdown of bradykinin in the airway

ACE does two jobs: it makes angiotensin II and it breaks down bradykinin. Inhibit the enzyme and you get both consequences, so bradykinin accumulates in the airways and provokes cough. ARBs block the receptor instead of the enzyme, leave bradykinin breakdown intact, and therefore do not cause it.

Answer: Heparin acts at once and is reversed with protamine

Heparin potentiates antithrombin directly, so the effect is immediate, measured by aPTT and reversed by protamine. Warfarin blocks synthesis of new clotting factors, so it cannot work until existing ones are cleared, which is why it takes days, is measured by INR and is reversed with vitamin K.

Answer: Falling potassium increases digoxin binding and toxicity

Digoxin and potassium compete for the same site on the Na⁺/K⁺-ATPase. Loop diuretics waste potassium, and as plasma potassium falls, less of it is there to compete, so digoxin binds more and its effect rises without the dose changing. The narrow therapeutic index turns that into toxicity.

Answer: Rapid clearance, giving a half-life of a few hours

Amiodarone is the opposite of rapidly cleared: it is highly lipophilic, accumulates in tissue and has a half-life measured in weeks. That single pharmacokinetic fact explains the rest of its reputation, because a drug lingering in thyroid, lung and eye for months has time to cause damage there.

Answer: Both raise cyclic GMP, so vasodilation compounds

Nitrates donate nitric oxide, which drives cGMP production; PDE5 inhibitors block the enzyme that degrades cGMP. Increase production and block removal of the same second messenger and the vasodilation compounds rather than adds, which can drop blood pressure dangerously.

Answer: Arteriolar dilation raises capillary pressure locally

Dihydropyridines dilate arterioles much more than venules, so capillary hydrostatic pressure rises and fluid is pushed into the tissue. Because total body fluid is normal, this oedema responds poorly to a diuretic, which is the clinical clue that distinguishes it from heart failure.

Answer: Also binds androgen and progesterone receptors

Spironolactone is a steroid, and its resemblance to other steroid hormones means it is not selective for the mineralocorticoid receptor. Off-target binding at androgen receptors produces the endocrine side effects. Eplerenone was designed with better receptor selectivity and largely avoids them.

Answer: Bisoprolol, which has high β₁ affinity

Bisoprolol, along with atenolol and metoprolol, has much higher affinity for β₁ than β₂, which makes it the safer choice where airway disease is a concern. Selectivity is relative and dose-dependent, not absolute: push the dose high enough and β₂ blockade appears anyway.

Answer: Report unexplained muscle pain; beware CYP3A4 inhibitors

Myopathy matters because it can progress to rhabdomyolysis, and its risk rises with statin plasma concentration. Most statins are CYP3A4 substrates, so anything inhibiting that enzyme raises the level and the risk, which is the reason grapefruit gets a mention it would not otherwise deserve.