Pharmacokinetics, Drug Interactions, Enzyme Induction

A 48-year-old woman with normal renal and hepatic function is prescribed a drug with a volume of distribution (Vd) of 0.5 L/kg, protein binding of 95%, and renal clearance accounting for 80% of total body clearance. She is also on oral contraceptives (OCP). After 2 weeks of therapy, her serum drug levels are subtherapeutic despite adherence. Which of the following mechanisms BEST explains the reduced drug efficacy?