Which statement best describes carbamazepine’s pharmacokinetic property related to dose planning?

• A. Carbamazepine's autoinduction means its own metabolism increases over time, often requiring dose adjustments.
• B. It does not induce enzymes
• C. It reduces absorption of other drugs
• D. It increases renal excretion of water

Answer: (C)

Carbamazepine is a strong hepatic enzyme inducer and it autoinduces its own metabolism. This means that over the first weeks of treatment, the drug’s clearance increases, causing its blood levels to drop unless the dose is raised. When planning dosing, you need to anticipate this autoinduction and adjust the dose to maintain seizure control. Additionally, by inducing the enzymes that metabolize other drugs, carbamazepine can lower the levels of co‑administered medications, which may require dose adjustments of those drugs. Its main effect isn’t reduced absorption in the gut or increased renal excretion of water, and it does induce enzymes, so statements claiming otherwise don’t fit the key dose‑planning concept.