Autoinduction as which response?

• A. Lower-than-expected drug levels
• B. Higher-than-expected drug levels
• C. No change in drug levels
• D. Toxic levels

Answer: (A)

Autoinduction happens when a drug increases the activity of the enzymes that metabolize it, usually hepatic cytochrome P450. Because those enzymes are upregulated, the drug is cleared more quickly over time. As a result, plasma levels fall below what you’d expect based on the initial dose—lower-than-expected drug levels. This is why dosing often needs to be adjusted upward after the induction period to maintain a therapeutic effect. Classic examples include carbamazepine, phenytoin, and phenobarbital, with the induction taking place over days to weeks. Autoinduction does not cause higher or unchanged levels, and it isn’t about reaching toxic levels unless dosing doesn’t account for the increased clearance.