A patient takes hydrochlorothiazide for hypertension. All of the following are expected effects of this drug EXCEPT:

Correct answer: B. Reflex tachycardia as a primary drug effect

• A. Hypokalemia is the classic metabolic adverse effect of thiazides, along with hyperuricemia, hyperglycemia, hypercalcemia and hyponatremia.
• B. CORRECT as the EXCEPTION. Thiazides do not characteristically produce TACHYCARDIA. They lower blood pressure by natriuresis and by reducing peripheral vascular resistance, and heart rate is essentially unchanged. Reflex tachycardia is the hallmark of direct arterial vasodilators such as hydralazine and of short-acting dihydropyridines, not of thiazide diuretics.
• C. Orthostatic hypotension is a well-recognized effect from volume depletion. Dentally this matters: raise the chair SLOWLY at the end of the appointment to avoid a syncopal episode.
• D. Increased urinary frequency is the expected direct effect — thiazides inhibit the Na⁺/Cl⁻ cotransporter in the distal convoluted tubule, increasing sodium and water excretion. Patients should be told to take the dose in the morning.

Note: Chairside relevance: thiazides cause xerostomia, orthostatic hypotension and hypokalemia. Raise the chair slowly, and remember that hypokalemia potentiates digoxin toxicity.