Cause of Hypokalemia in This Patient
The thiazide diuretic is the cause of this patient's hypokalemia. 1, 2
Mechanism of Thiazide-Induced Hypokalemia
Thiazide diuretics cause hypokalemia through two primary mechanisms 3:
Increased distal sodium delivery: Thiazides inhibit the sodium-chloride transporter in the distal tubule, leading to increased sodium delivery to the cortical collecting duct with consequent increased potassium excretion via ROMK2 channels to maintain electrical neutrality 4, 1
Secondary hyperaldosteronism: The diuretic-induced natriuresis causes upregulation of aldosterone-sensitive ENaC channels, which further enhances potassium loss and can persist for 24 hours or longer—well beyond the period of active diuresis 4, 3
Why Not the Other Medications?
ACE Inhibitors actually prevent hypokalemia rather than cause it 1, 5. ACE inhibitors reduce renal potassium losses by blocking the renin-angiotensin-aldosterone system, and patients taking them may not require routine potassium supplementation 5. In fact, combining ACE inhibitors with thiazides helps counterbalance the potassium-depleting effects 2, 6.
Beta blockers do not cause hypokalemia 4. While they can affect renal perfusion through reduced cardiac output, this does not translate into clinically significant potassium wasting 4.
Salbutamol causes transient intracellular potassium shifts (moving potassium into cells temporarily) but does not cause true potassium depletion or chronic hypokalemia 1. The hypokalemia from beta-agonists resolves once the medication effect wears off and does not result in total body potassium deficit 5.
Clinical Correlation
The presentation of dizziness and muscle cramps is classic for thiazide-induced hypokalemia 6, 7. Thiazides are among the most common causes of hypokalemia in clinical practice, with prevalence ranging from 7-56% in patients taking these medications 6. The severity correlates with dose, with higher doses causing more profound potassium depletion 8, 9.
Important Clinical Caveat
The potassium loss from thiazides exceeds the period of active diuresis because elevated aldosterone levels persist for 24+ hours after the diuretic effect wanes 3. This means patients continue losing potassium even when they're no longer experiencing increased urination, making this a particularly insidious cause of hypokalemia that requires monitoring and often supplementation or addition of potassium-sparing agents 1, 2.
Answer: C. Thiazide diuretic