Effects of Highly Active Antiretroviral Therapy on Renal Function and Renal Phosphate Handling in African Adults with Advanced HIV and CKD

Background: Highly Active Antiretroviral Therapy (HAART) has been implicated in renal dysfunction with hypophosphataemia. Objective: We prospectively evaluated renal phosphate excretion during HAART use. Method: Newly diagnosed human immunodeficiency virus (HIV)-infected individuals were treated with Tenofovir disoproxil fumarate/Emtricitabine/Efavirenz (TDF/FTC/EFV), n=33; Zidovudine/Lamivudine/Nevirapine (ZDV/3TC/NVP), n=53; and Zidovudine/Lamivudine/Efavirenz (ZDV/3TC/EFV), n=16. Creatinine and phosphate were assayed in blood and urine simultaneously at baseline, 1, 3, 6 and 9 months. Glomerular filtration rate (eGFR), fractional phosphate excretion and reabsorption (FEPi % and TRP), and the ratio of tubular maximum reabsorption of phosphate (TmP) to GFR (TmP/GFR) were estimated. Results: At baseline, eGFR showed moderate chronic kidney disease (mean: 35.50 ± 2.02, 33.14 ± 1.63, and 39.97±1.84 ml/min/1.73m2 in the 3 groups respectively); 54 (52.9%) patients had hyperphosphataemia (>1.4mmo/L); 43 (42.2%) had normophosphataemia (0.6-1.4mmol/L); 5 (4.9%) had hypophosphataemia (<0.6mmol/L). eGFR improved significantly from 1 month (≥60, 58.65 ± 1.11, and 51.76 ±1.59 ml/min/1.73m2; p=0.04, <0.001, 0.67 respectively), with a relapse at 9 months in TDFtreated subjects (50.10 ± 1.89 ml/min/1.73m2). TDF/FTC/EFV resulted in significantly greater reduction in plasma phosphate than ZDV/3TC/NVP (p=0.031), but not significantly different from ZDV/3TC/EFV (p=0.968). Similarly, ZDV/3TC/EFV resulted in significantly greater reduction in plasma phosphate than ZDV/3TC/NVP (p=0.036). FEP% progressively increased with HAART duration, more in TDF-treated and ZDV/3TC/EFV-treated groups than ZDV/3TC/NVP (p=0.014); TRP was elevated (>0.86), implying non-maximal phosphate reabsorption. TmP/GFR values were elevated, (>1.35mmol/l). Conclusion: HIV causes kidney dysfunction with reduced phosphate excretion resulting in hyperphosphataemia but HAART improves renal function. Prolonged use of TDF can cause renal toxicity with hypophosphataemia as fractional excretion progressively increased with duration of therapy unlike ZDV/3TC/NVP. The use of different third agents (either NVP or EFV) in zidovudine-based therapy results in significantly different plasma phosphate levels; ZDV/3TC/EFV, like TDF/FTC/EFV, resulted in significantly greater decline in plasma phosphate than ZDV/3TC/NVP. Thus, Evafirenz (EVF) may have similar or synergistic adverse effects with tenofovir disoproxil fumarate (TDF).