A patient taking fexofenadine for allergic rhinitis drinks large quantities of grapefruit juice daily and reports poor symptom control. The interaction responsible involves reduced intestinal absorption of fexofenadine via inhibition of:

• A CYP3A4 in enterocytes
• B Gastric H+/K+ ATPase
• C P-glycoprotein efflux pump
• D OATP1A2 organic anion uptake transporter ✓

Explanation

Fexofenadine absorption depends on the uptake transporter OATP1A2 (organic anion transporting polypeptide) in the intestinal epithelium. Components of grapefruit and apple juice inhibit OATP-mediated uptake, lowering plasma concentrations and therapeutic effect. This contrasts with terfenadine, whose problem was CYP3A4 blockade causing cardiotoxic accumulation; fexofenadine undergoes negligible CYP metabolism. P-glycoprotein inhibition would increase, not decrease, exposure. The practical teaching point is to separate fruit juices from fexofenadine dosing.

Reference: Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.