A patient on tenofovir alafenamide (TAF)-based ART regimen has significantly less renal and bone toxicity compared to tenofovir disoproxil fumarate (TDF). The pharmacological basis for this differential toxicity profile is:

• A TAF achieves higher intracellular tenofovir diphosphate concentrations in lymphocytes with substantially lower plasma tenofovir levels, reducing renal tubular and osteoblast exposure ✓
• B TAF is a tenofovir prodrug that is only activated inside CD4+ T-cells and not metabolized in kidney or bone cells
• C TDF but not TAF is transported into proximal tubular cells by organic anion transporters OAT1/3
• D TAF inhibits mitochondrial toxicity pathways in bone cells that TDF activates via polymerase gamma inhibition

Explanation

TAF is a phosphonamidate prodrug with improved intracellular activation compared to TDF; TAF is converted to tenofovir alafenamide intracellularly by cathepsin A in lymphocytes, generating high levels of active tenofovir diphosphate (TFV-DP) inside cells at doses 10-fold lower than TDF. Because TAF requires less parent compound in plasma to achieve equivalent virological suppression, circulating plasma tenofovir concentrations are 90% lower than TDF — this dramatically reduces drug delivery to proximal renal tubular cells (nephrotoxicity) and to bone-resorbing osteoclasts (reduced bone mineral density loss).

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.