Low-dose ritonavir is included in some protease inhibitor regimens even though its antiretroviral contribution at that dose is minimal. The pharmacological rationale for including it is:

• A It induces CYP3A4 and accelerates clearance of the companion drug
• B It inhibits CYP3A4 and reduces first-pass metabolism of the companion protease inhibitor ✓
• C It blocks P-glycoprotein efflux in the central nervous system
• D It competes with the companion drug for renal organic cation transporters

Explanation

Ritonavir is a potent CYP3A4 inhibitor. At low 'boosting' doses it reduces the hepatic and intestinal first-pass metabolism of co-administered protease inhibitors, raising their trough concentrations, allowing less frequent dosing and increasing the genetic barrier to resistance. Induction would do the opposite of what is intended, eliminating option A.

Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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