Pharmacology CMS Practice Test

Lithium is cleared by the kidneys and its level in the blood is very sensitive to changes in kidney function and sodium balance. It is filtered and then reabsorbed in the proximal tubule along with sodium, so anything that reduces kidney filtration or alters sodium handling can raise lithium levels and increase toxicity risk. NSAIDs or aspirin are particularly important here because they decrease prostaglandin synthesis in the kidney, which lowers renal perfusion and glomerular filtration. With less filtration, lithium reabsorption in the proximal tubule increases, leading to higher serum lithium concentrations and a greater danger of toxicity (tremor, confusion, ataxia, seizures, etc.). That’s why these drugs should be avoided or used with caution in someone taking lithium, and an alternative pain reliever like acetaminophen is often recommended unless a clinician advises otherwise. Maintaining a stable salt intake and adequate hydration helps keep lithium levels steadier, since significant changes in sodium balance can also shift lithium reabsorption. Regular exercise is generally fine, and daily vitamin C isn’t a major concern with lithium. So the reason the best choice is the NSAIDs or aspirin is their direct impact on kidney function and lithium clearance, increasing the risk of toxicity.