Antihypertensive Drugs

Correct Answer

C — Amlodipine — dihydropyridine; acts predominantly on vascular smooth muscle with minimal direct cardiac effects

Rationale

Amlodipine is a dihydropyridine calcium channel blocker with high vascular-to-cardiac selectivity. It binds preferentially to L-type calcium channels in vascular smooth muscle, producing potent arteriolar vasodilation with minimal effects on heart rate, atrioventricular conduction, or myocardial contractility at therapeutic doses. This makes it safe in heart failure with reduced ejection fraction and in combination with rate-controlling agents. Verapamil and diltiazem are non-dihydropyridines with approximately equal effects on vascular and cardiac tissue — they slow sinoatrial node automaticity, atrioventricular node conduction, and reduce myocardial contractility. The subclass distinction determines virtually all clinically important differences in safety, indications, and contraindications between the calcium channel blockers.

Correct Answer

A — Thiazide-like diuretic

Rationale

Chlorthalidone is a thiazide-like diuretic. Furosemide is a loop diuretic. Amiloride is a potassium-sparing diuretic. Acetazolamide is a carbonic anhydrase inhibitor.

Correct Answer

B — Non-dihydropyridine calcium channel blockers

Rationale

Verapamil is a non-dihydropyridine calcium channel blocker, along with diltiazem. Amlodipine and nifedipine are dihydropyridine calcium channel blockers.

Correct Answer

D — Potassium-sparing diuretics

Rationale

Amiloride and triamterene are potassium-sparing diuretics that act independently of aldosterone receptor blockade. Furosemide is a loop diuretic. Hydrochlorothiazide is a thiazide diuretic. Spironolactone and eplerenone are aldosterone antagonists, a distinct potassium-sparing subclass.

Correct Answer

C — Loop diuretics

Rationale

Torsemide and furosemide are both loop diuretics. Hydrochlorothiazide is a thiazide diuretic. Amiloride is a potassium-sparing diuretic. Spironolactone is an aldosterone antagonist.

Correct Answer

A — Thiazide-like diuretic

Rationale

Indapamide is a thiazide-like diuretic. Bumetanide is a loop diuretic. Triamterene is a potassium-sparing diuretic. Eplerenone is a mineralocorticoid receptor antagonist.

Correct Answer

B — The edema results from increased capillary hydrostatic pressure caused by arteriolar dilation, not sodium and water retention, so diuresis does not address the underlying mechanism

Rationale

Dihydropyridine calcium channel blockers selectively dilate arterioles without a corresponding effect on venules or the venous side of the circulation. This preferential arteriolar dilation increases capillary hydrostatic pressure by reducing the resistance upstream of the capillary bed, forcing fluid into the interstitium of dependent tissues — producing the characteristic ankle and lower leg edema. Because the mechanism is hemodynamic rather than sodium-mediated, diuretics remove intravascular fluid but cannot reduce the elevated capillary hydrostatic pressure that drives ongoing fluid accumulation in the interstitium. A more effective approach is to add a renin-angiotensin-aldosterone system inhibitor, which dilates both arterioles and the efferent arteriole and also produces some venodilation, reducing capillary hydrostatic pressure. Dose reduction or switching to a different drug class is also an option if the edema is clinically troublesome.

Correct Answer

D — Both non-dihydropyridines and beta-adrenergic receptor antagonists suppress sinoatrial and atrioventricular nodal conduction, and combining them risks severe bradycardia, complete heart block, or asystole

Rationale

Non-dihydropyridine calcium channel blockers — verapamil and diltiazem — slow sinoatrial node automaticity and atrioventricular node conduction through L-type calcium channel blockade in cardiac nodal tissue. Beta-adrenergic receptor antagonists slow the same nodes through a different mechanism: blocking the beta-1 receptors through which catecholamines accelerate nodal activity. When both drug classes are given together, their effects on nodal conduction are additive. The combination can produce profound bradycardia, high-degree atrioventricular block, or complete atrioventricular dissociation leading to asystole. This combination is therefore contraindicated. The safe alternative is to use a dihydropyridine calcium channel blocker such as amlodipine, which lacks significant cardiac nodal effects and can be safely combined with beta-adrenergic receptor antagonists.

Correct Answer

A — Thiazides increase sodium delivery to the collecting duct, stimulating aldosterone-mediated potassium secretion; hypomagnesemia co-occurs because magnesium depletion impairs renal potassium conservation

Rationale

Thiazides block sodium reabsorption in the distal convoluted tubule, increasing the amount of sodium reaching the collecting duct. In the collecting duct, aldosterone drives sodium reabsorption through epithelial sodium channels in exchange for potassium secretion into the tubular lumen. More sodium delivery means more aldosterone-driven potassium loss. Hypomagnesemia commonly accompanies thiazide-induced hypokalemia and is clinically important: magnesium is required for renal tubular potassium reabsorption, and when magnesium is depleted, the kidney cannot conserve potassium even if serum levels are low. Correcting magnesium depletion is often necessary before potassium levels can be restored. Clinicians should therefore check both electrolytes in patients on thiazide therapy who develop hypokalemia, and replace magnesium alongside potassium when both are deficient.

Correct Answer

C — Recurrent calcium nephrolithiasis, where thiazides reduce urinary calcium excretion and lower the risk of calcium stone formation

Rationale

Thiazides enhance calcium reabsorption in the distal convoluted tubule, reducing urinary calcium excretion (hypocalciuria). This is directly opposite to the effect of loop diuretics, which increase urinary calcium loss. The reduction in urinary calcium makes thiazides useful in patients with hypercalciuria-related recurrent calcium oxalate or calcium phosphate kidney stones — by lowering the urinary calcium concentration, the supersaturation that drives stone nucleation is reduced. Thiazides may also provide some protection against osteoporotic fractures through reduced calcium loss, but they are not first-line pharmacological therapy for osteoporosis. Loop diuretics such as furosemide are sometimes used acutely in hypercalcemia of malignancy because they promote urinary calcium excretion — the opposite of thiazide action.

Correct Answer

B — The renin-angiotensin-aldosterone system inhibitor blunts the reactive renin-angiotensin-aldosterone system activation triggered by calcium channel blocker-induced vasodilation and reduces the peripheral edema that calcium channel blockers cause by increasing venous and efferent arteriolar tone

Rationale

The calcium channel blocker plus renin-angiotensin-aldosterone system inhibitor pairing is physiologically synergistic in two important ways. First, arteriolar vasodilation from the calcium channel blocker activates the renin-angiotensin-aldosterone system reflexively; the renin-angiotensin-aldosterone system inhibitor blunts this activation, preventing the counter-regulatory rise in angiotensin II and aldosterone that would otherwise partially offset the blood pressure reduction. Second, the renin-angiotensin-aldosterone system inhibitor dilates efferent arterioles and has some venodilatory effect, which reduces the elevated capillary hydrostatic pressure responsible for dihydropyridine-induced peripheral edema — each drug reduces a side effect of the other. The combination was compared directly with a calcium channel blocker plus thiazide in a large cardiovascular outcome trial involving high-risk patients, and the calcium channel blocker plus renin-angiotensin-aldosterone system inhibitor regimen produced a 20 percent reduction in cardiovascular events despite similar blood pressure lowering in both groups.

Correct Answer

D — Mineralocorticoid receptor antagonists such as spironolactone; because resistant hypertension frequently involves unsuspected aldosterone excess and sodium retention that targeted receptor blockade directly addresses

Rationale

A landmark trial comparing spironolactone, bisoprolol, and doxazosin as fourth-line agents in resistant hypertension found that spironolactone produced the greatest blood pressure reduction of the three, establishing it as the preferred fourth-line agent. The mechanistic explanation is that resistant hypertension disproportionately involves elevated aldosterone activity — either from primary aldosteronism (diagnosed or unrecognized) or from secondary aldosterone excess driven by the renin-angiotensin-aldosterone system. Patients already on three agents are often still retaining sodium through aldosterone-mediated mechanisms despite standard diuretic therapy, because thiazides do not block the collecting duct mineralocorticoid receptor where aldosterone acts. Spironolactone directly blocks mineralocorticoid receptors, removing the aldosterone-driven sodium retention at its source. Obstructive sleep apnea — which is also associated with aldosterone excess — is overrepresented in resistant hypertension, further explaining spironolactone's efficacy in this population.

Correct Answer

A — Immediate-release nifedipine causes abrupt vasodilation that triggers reflex sympathetic activation with tachycardia, which has been associated with adverse cardiovascular outcomes; extended-release formulations achieve gradual, sustained vasodilation that avoids this reflex

Rationale

Immediate-release nifedipine is rapidly absorbed and produces a sharp peak in plasma concentration, causing abrupt and intense arteriolar vasodilation. This sudden drop in blood pressure triggers a powerful reflex sympathetic response — tachycardia, increased myocardial contractility, and catecholamine surge — that can precipitate myocardial ischemia in patients with coronary artery disease. The rapid blood pressure swings associated with immediate-release nifedipine have been associated with adverse cardiovascular outcomes in clinical studies. Extended-release formulations (gastrointestinal therapeutic system and extended-release capsules) deliver nifedipine gradually, maintaining steady plasma levels without the sharp peak and producing sustained vasodilation without triggering the reflex sympathetic surge. This distinction is specific to nifedipine among dihydropyridines because other agents in the class such as amlodipine are inherently long-acting by virtue of their pharmacokinetics and are not available in short-acting forms for hypertension.

Correct Answer

C — Loop diuretics; as estimated glomerular filtration rate falls below approximately 30 mL per minute, the reduced filtered sodium load reaching the distal convoluted tubule diminishes the natriuretic effect of thiazides, while loop diuretics acting at the thick ascending limb remain effective

Rationale

Thiazide diuretics block the sodium-chloride cotransporter in the distal convoluted tubule, a segment that handles only about 5 to 10 percent of filtered sodium under normal conditions. When glomerular filtration rate is reduced, less sodium is filtered overall, and much of what is filtered is reabsorbed proximally — leaving little sodium to reach the distal convoluted tubule for thiazides to act upon. The result is markedly diminished natriuretic efficacy. Loop diuretics act in the thick ascending limb of the loop of Henle, which handles approximately 25 percent of filtered sodium. This segment remains active even at low glomerular filtration rates, and loop diuretics retain meaningful diuretic efficacy. Furosemide and torsemide are therefore the preferred agents for volume management and blood pressure control in advanced chronic kidney disease. Potassium-sparing agents require caution in this population because reduced renal potassium excretion capacity amplifies the risk of hyperkalemia.

Correct Answer

D — Add a renin-angiotensin-aldosterone system inhibitor, which reduces capillary hydrostatic pressure through efferent arteriolar and venous dilation — more effective than diuretics for hemodynamically driven edema

Rationale

Amlodipine dilates arterioles without a corresponding effect on the venous side of the circulation, raising capillary hydrostatic pressure and pushing fluid into the interstitium of dependent tissues. Because this edema is hemodynamic in origin — not caused by sodium and water retention — diuretics remove intravascular fluid but cannot reduce the elevated capillary pressure that drives ongoing fluid accumulation. Renin-angiotensin-aldosterone system inhibitors are more effective because they produce efferent arteriolar and some venous dilation, which lowers capillary hydrostatic pressure directly. This combination also provides the additional pharmacological benefit of blunting the reactive renin-angiotensin-aldosterone system activation triggered by amlodipine-induced vasodilation. The calcium channel blocker plus renin-angiotensin-aldosterone system inhibitor pairing is both mechanistically synergistic and supported by cardiovascular outcome evidence, making it a preferred dual regimen. Switching to verapamil would trade one set of problems for another, including constipation, cardiac depression, and drug interaction risks.

Correct Answer

B — Both diltiazem and metoprolol suppress sinoatrial and atrioventricular nodal conduction, and combining them risks additive bradycardia, complete heart block, or asystole

Rationale

Diltiazem is a non-dihydropyridine calcium channel blocker that slows sinoatrial node automaticity and atrioventricular node conduction by blocking L-type calcium channels in cardiac nodal tissue. Metoprolol is a selective beta-1 adrenergic receptor antagonist that slows the same nodes by blocking catecholamine-driven acceleratory signaling. When both are present simultaneously, their effects on nodal conduction are additive — neither drug alone may produce dangerous bradycardia, but together they can suppress nodal activity enough to cause profound bradycardia, high-degree atrioventricular block, or asystole. This is the mechanistic basis for the contraindication of combining non-dihydropyridine calcium channel blockers with any beta-adrenergic receptor antagonist. If both rate control and beta-blockade are needed, amlodipine can be substituted for diltiazem for blood pressure control, as dihydropyridines do not suppress cardiac nodal conduction and can be safely combined with beta-adrenergic receptor antagonists.

Correct Answer

A — Hydrochlorothiazide increases sodium delivery to the collecting duct, driving aldosterone-mediated potassium loss; and it reduces uric acid excretion by competing with urate for tubular secretion and by raising urate reabsorption through volume contraction

Rationale

Thiazide-induced hypokalemia occurs because blocking the sodium-chloride cotransporter in the distal convoluted tubule increases the sodium load reaching the collecting duct. Aldosterone in the collecting duct drives sodium reabsorption through epithelial sodium channels in exchange for potassium secretion — more sodium delivery means more potassium is lost in the urine. Thiazide-induced hyperuricemia occurs through two simultaneous mechanisms: first, thiazide molecules compete with urate for the same proximal tubular secretory transporter, reducing uric acid excretion; second, the mild volume contraction caused by diuresis raises urate reabsorption in the proximal tubule. When uric acid accumulates to supersaturation in joint fluid, monosodium urate crystals precipitate, triggering acute gout. In patients with gout or hyperuricemia who need a renin-angiotensin-aldosterone system inhibitor as a partner drug, losartan is the preferred choice because it inhibits urate transporter 1 and provides a mild uricosuric effect that partially counteracts thiazide-driven uric acid retention.

Correct Answer

C — Replace chlorthalidone with a loop diuretic, because thiazide efficacy is markedly reduced when estimated glomerular filtration rate falls below approximately 30 mL per minute and loop diuretics acting at the thick ascending limb retain effectiveness at this level

Rationale

At an estimated glomerular filtration rate of 22 mL per minute per 1.73 m², the amount of sodium filtered by the glomerulus is substantially reduced, and a larger fraction of what is filtered is reabsorbed proximally before reaching the distal convoluted tubule. Thiazide diuretics, which act at the distal convoluted tubule, find relatively little sodium to block — their natriuretic effect is therefore markedly diminished. Loop diuretics act at the thick ascending limb of the loop of Henle, which handles a larger fraction of the total sodium reabsorption. The thick ascending limb remains active and accessible to loop diuretics even at markedly reduced estimated glomerular filtration rates, making furosemide or torsemide the appropriate switch in this patient. Spironolactone should be used with great caution in advanced chronic kidney disease because the already-reduced capacity for renal potassium excretion is further impaired, substantially raising the risk of life-threatening hyperkalemia.