Question:
Which of the following antihypertensive drugs is contraindicated in a patient on lithium therapy in order to prevent toxicity?
Which of the following antihypertensive drugs is contraindicated in a patient on lithium therapy in order to prevent toxicity?
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Sodium and volume depletion make the kidney reabsorb more lithium.
Updated On: Jun 24, 2026
- Clonidine
- Beta blockers
- Calcium channel blockers
- Diuretics
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The Correct Option is D
Solution and Explanation
Step 1: Lithium is handled by the kidney almost like sodium. It is freely filtered and largely reabsorbed in the proximal tubule, with no protein binding and no hepatic metabolism, so renal clearance determines its blood level.
Step 2: Diuretics (especially thiazides) cause sodium and volume depletion. The proximal tubule compensates by enhancing sodium reabsorption, and because lithium follows the same pathway, lithium reabsorption also rises. The result is reduced lithium excretion and accumulation toward toxic levels.
Step 3: Lithium has a narrow therapeutic index, so even a modest fall in clearance can precipitate toxicity (tremor, confusion, seizures, arrhythmias). Hence diuretics are the antihypertensive class to avoid.
Step 4: The other options are comparatively safe in this respect: Clonidine (central alpha-2 agonist), Beta blockers and Calcium channel blockers do not significantly impair lithium clearance, although verapamil/diltiazem need monitoring.
Conclusion: The correct answer is Diuretics, matching the printed key.
Step 2: Diuretics (especially thiazides) cause sodium and volume depletion. The proximal tubule compensates by enhancing sodium reabsorption, and because lithium follows the same pathway, lithium reabsorption also rises. The result is reduced lithium excretion and accumulation toward toxic levels.
Step 3: Lithium has a narrow therapeutic index, so even a modest fall in clearance can precipitate toxicity (tremor, confusion, seizures, arrhythmias). Hence diuretics are the antihypertensive class to avoid.
Step 4: The other options are comparatively safe in this respect: Clonidine (central alpha-2 agonist), Beta blockers and Calcium channel blockers do not significantly impair lithium clearance, although verapamil/diltiazem need monitoring.
Conclusion: The correct answer is Diuretics, matching the printed key.
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