Which drug interactions are listed as precipitating lithium toxicity?

• A. NSAIDs, ACE inhibitors, and thiazides
• B. SSRIs only
• C. Antipsychotics only
• D. Antibiotics only

Answer: (A)

The fundamental idea is that lithium toxicity is driven by higher lithium levels in the blood, which happen when its renal clearance is reduced. Lithium is cleared by the kidneys and behaves similarly to sodium, so anything that shifts sodium handling or lowers kidney filtration can raise lithium levels and provoke toxicity.

NSAIDs block renal prostaglandin synthesis, which constricts the afferent arteriole and lowers glomerular filtration. That reduction in filtration slows lithium clearance, increasing its concentration.

Thiazide diuretics increase sodium reabsorption in the proximal tubule, and because lithium follows sodium, more lithium is reabsorbed back into the bloodstream. This raises lithium levels and the risk of toxicity.

ACE inhibitors alter renal hemodynamics and sodium handling in a way that can further reduce lithium clearance, again raising serum levels.

These are the classic, well-established interactions that precipitate lithium toxicity. The other options don’t capture this combination of drug classes that reliably increases lithium levels.

So the best choice lists NSAIDs, ACE inhibitors, and thiazides.