Autoinduction yields which observation?

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

Answer: (A)

Autoinduction occurs when a drug stimulates the production of enzymes that metabolize it, usually in the liver. That means the drug speeds up its own metabolism over time, so clearance increases and plasma concentrations drop compared with what you’d expect from the same dose earlier in therapy. Because of this, you often see lower-than-expected drug levels after steady state has been reached, sometimes necessitating a higher dose to maintain therapeutic effect. This slower-to-reach-or-maintain level explains why the observation is subtherapeutic rather than higher, unchanged, or toxic.