What is a typical clinical consequence of auto-induction?

• A. Decreased exposure
• B. Increased exposure
• C. No change
• D. Increased half-life

Answer: (A)

Auto-induction occurs when a drug increases the activity of enzymes that metabolize it, usually hepatic enzymes. Over time this raises clearance, so the drug is eliminated faster. As clearance goes up, the body's exposure to the drug falls unless the dose is increased to compensate. In practical terms, repeated dosing leads to lower plasma concentrations and a smaller overall AUC. The apparent half-life tends to shorten because higher clearance speeds up elimination.

Rifampin is a classic example—start therapy and the drug’s own metabolism ramps up, reducing its exposure unless you titrate the dose. Increased exposure or no change would imply the opposite effect on metabolism, and a longer half-life would require slower clearance, which auto-induction does not cause.