The half-life of carbamazepine is __________ hours.

• A. 6
• B. 24
• C. 12
• D. 48

Answer: (C)

The main idea here is how carbamazepine is cleared from the body and how that changes with continued use. Carbamazepine autoinduces hepatic enzymes, so as you treat someone over several days to weeks, the liver becomes more efficient at metabolizing it. That means the drug’s half-life drops from its initial, longer value to a shorter, steady-state value. In practice, the half-life at steady state is typically around 12 hours (often described as roughly 12 to 17 hours). This makes 12 hours the best representative number among common choices, and it also explains why dosing is often done every 12 hours to maintain stable levels. The other options don’t fit with this pattern: a 6-hour half-life would imply faster clearance than is usually seen after autoinduction, while 24 or 48 hours are longer than the typical autoinduced half-life.