However, at 4 weeks a new “set point” was reached, with minimal subsequent change up to week 96 (−2.6 vs. −1.0 mL/min for Stribild and Atripla in the 0102 study, −1.8 vs. −4.4 mL/min for Stribild and TDF/FTC/ATV/RTV in the 0103 study) [18, 19]. In the 0114 study, patients in the COBI arm experienced greater

reductions in creatinine clearance (−13 vs. −9 mL/min) than in the RTV arm [33]. Five patients (1.4%) check details in the 0102 study, all in the Stribild arm, had renal events (reported as elevated serum creatinine in two, renal failure in two, Fanconi syndrome in one; a total of four patients had evidence of proximal tubulopathy that led to study drug discontinuation before week 48) [29]. Further two patients (0.6%) in the Stribild arm discontinued study drug between weeks 48 and 96, because of renal adverse events consisting of serum creatinine elevations not accompanied by proximal tubulopathy [31]. In the 0103 study, five patients (Stribild arm ABT-199 price 3, ATV/RTV arm 2) discontinued study drug due to renal events before week 96; none had evidence of proximal tubulopathy [32]. In the 0114 study, 1.7% and 1.4% of patients discontinued study medication for renal

events in the COBI and RTV arms, and 5 vs. 2 cases had proximal tubulopathy [33]. The low rate of renal discontinuations and renal tubular disease suggests an overall favourable renal safety profile of Stribild and COBI. Indeed, data from patients with creatinine clearance 50–89 mL/min who initiated Stribild Oxymatrine or substituted RTV with COBI observed no increased rate of renal toxicity or renal discontinuations [36]. The increases in serum creatinine concentration and the reductions in estimates of creatinine clearance and glomerular filtration rate are unlikely to be of clinical importance. Some of the renal discontinuations were likely to be due to patients meeting pre-specified criteria for discontinuation

rather than secondary to overt renal toxicity. Nonetheless, the population included in the clinical trials was at low risk of kidney injury and despite this a small number developed significant renal tubular disease requiring drug discontinuation. The risk factors for TDF-induced Fanconi syndrome and renal tubular disease remain poorly defined but may point to an interaction between COBI and tenofovir at renal tubular level, as previously suggested for RTV [37]. Although such an interaction is not predicted by in vitro studies (Fig. 1), clinicians will need to remain alert to the nephrotoxic potential of Stribild in clinical practice. Fig. 1 Effect of various drugs on tubular creatinine secretion [17]. Tubular secretion of creatinine and tenofovir is mediated through distinct membrane transporter molecules. Based on in vitro experiments, no interaction between cobicistat and tenofovir is predicted.