A patient with bipolar disorder has only 40% renal function following a lithium overdose. What will be most affected?

Correct answer: C. Drug excretion

• A. Gastric emptying is a GI motility function, unrelated to renal clearance.
• B. Absorption occurs in the GI tract and is not governed by renal function.
• C. Correct. Lithium is eliminated essentially unchanged by the kidney and is not metabolized. Reduced GFR means reduced clearance, accumulation and toxicity — dose adjustment is required for renally excreted drugs, and NSAIDs must be avoided since they raise lithium levels.
• D. Protein binding is primarily determined by plasma albumin and hepatic synthesis.