Tenofovir alafenamide (TAF) was developed to replace tenofovir disoproxil fumarate (TDF) in HIV treatment. What pharmacokinetic advantage does TAF have over TDF that reduces nephrotoxicity and bone toxicity?

• A TAF is eliminated by hepatic metabolism rather than renal clearance, bypassing kidney tubular toxicity
• B TAF does not require phosphorylation and acts directly as a nucleotide analogue at lower tissue concentrations
• C TAF binds renal tubular transporters (OAT1) with lower affinity than TDF, reducing intracellular accumulation in proximal tubule cells
• D TAF is more rapidly activated intracellularly in lymphocytes, achieving higher intracellular concentrations of tenofovir diphosphate at 90% lower plasma tenofovir concentrations, dramatically reducing renal and bone exposure to free tenofovir ✓

Explanation

TDF is cleaved in plasma and various tissues to produce tenofovir, which enters cells; high systemic tenofovir levels cause proximal tubular toxicity (Fanconi syndrome) and reduce bone mineral density. TAF is a lipophilic phosphonamidate prodrug that is stable in plasma and preferentially cleaved inside lymphocytes (by cathepsin A), releasing high intracellular tenofovir concentrations with >90% lower plasma tenofovir levels than TDF. This dramatically reduces kidney tubular cell and bone exposure. Higher intracellular TFV-diphosphate (active form) in PBMC/lymphocytes is maintained at 4 mg TAF vs 300 mg TDF doses.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.