Why should a patient on lithium avoid calcium channel blockers?

Why should a patient on lithium avoid calcium channel blockers?

• A. Risk of fatal nephrotoxicity
• B. Increased lithium clearance
• C. Decreased serum lithium
• D. No interaction

Answer: (A)

Lithium is cleared by the kidneys and has a very narrow therapeutic window, so drugs that alter renal function or sodium handling can raise lithium levels. Calcium channel blockers can affect renal perfusion and tubular handling, reducing lithium clearance. When clearance drops, lithium accumulates and toxicity risk rises, including potential nephrotoxicity and even acute kidney injury, which can be life-threatening. That’s why this combination requires caution and monitoring. The other options don’t fit because the interaction does not typically increase clearance, decrease serum lithium, or imply no interaction.

Lithium is cleared by the kidneys and has a very narrow therapeutic window, so drugs that alter renal function or sodium handling can raise lithium levels. Calcium channel blockers can affect renal perfusion and tubular handling, reducing lithium clearance. When clearance drops, lithium accumulates and toxicity risk rises, including potential nephrotoxicity and even acute kidney injury, which can be life-threatening. That’s why this combination requires caution and monitoring. The other options don’t fit because the interaction does not typically increase clearance, decrease serum lithium, or imply no interaction.