Pharmacodynamic modeling suggests a bacterial strain inactivates 80% of administered ampicillin molecules by secreted beta-lactamase. If a beta-lactamase inhibitor reduces the enzyme's activity by 90%, what fraction of the original ampicillin remains active? (Assume linear inactivation and start with 100 units of active drug.)

• A. 8% remains active because the inhibitor blocks most antibiotic binding and accelerates drug loss, leaving a small fraction to act on PBPs.
• B. 100% remains active because clavulanate always fully restores antibiotic activity irrespective of enzyme levels; degradation is negligible afterward.
• C. 20% remains active because the inhibitor converts the enzyme effect to the value observed in stationary phase where only a fifth of drug reaches PBPs.
• D. 92% of the original drug remains active (92 units out of 100).

Answer: (D)