30-year-old woman was newly diagnosed with bipolar disorder.

Question

Her physician reviewed her current medication list before initiating treatment with lithium to ensure that she was not taking any drugs that could alter lithium levels. Drugs that affect which of the following are most likely to increase plasma levels of lithium?
A. Glomerular filtration.
B. Bile formation.
C. Muscarinic receptors.
D. Tyrosine iodination.
E. CYP2D6.

Answer 1

The correct answer is A. Glomerular filtration.

Lithium is primarily eliminated from the body through the kidneys, specifically by glomerular filtration. Medications that affect renal function, such as diuretics, NSAIDs, ACE inhibitors, and certain other drugs that may alter glomerular filtration rate, can lead to increased plasma levels of lithium. When glomerular filtration decreases, lithium clearance is reduced, leading to elevated plasma levels.

Other options listed (bile formation, muscarinic receptors, tyrosine iodination, and CYP2D6) do not directly influence lithium levels and are not relevant to its pharmacokinetics in terms of plasma concentration management.