Incidence of and risk factors for tenofovir-induced nephrotoxicity: a retrospective cohort study

Objectives Despite the recent publication of case reports describing various manifestations of tenofovir-related nephrotoxicity, data regarding the incidence of and risk factors for this adverse effect are currently lacking. Methods A retrospective cohort study of patients from four centres in Toronto, Canada, enrolled in the tenofovir expanded access programme with a minimum of 3 months follow up, was carried out. Results A total of 172 patients receiving tenofovir disoproxil fumarate (TDF) for a median of 16 months (range 3-25 months) were included in the study. Seven (4%) patients developed grade 1 (> 44 mu mol/ L from baseline) increases in serum creatinine (SCr) during follow up; no patient developed grade 2 or higher nephrotoxicity. Fifteen (8.7%) patients had an increase in SCr of greater than 1.5 times baseline values during follow up. Four (2.3%) patients discontinued TDF because of an increase in SCr and/or abnormal urinalysis. Of 62 patients with a urinalysis, grade 1 or higher proteinuria (< 3 g/L) was observed in 27 (43%) patients. Only baseline SCr [odds ratio (OR) = 0.51 per 10 pmol/L increase; P = 0.0005] and baseline creatinine clearance (1.26 per 10 mL/min increase; P=0.01) were significantly associated with ever having a 1.5-fold increase in serum creatinine. Twenty-eight (16%) and 11 (6%) patients developed grade 1 (serum phosphorus < 0.71 mmol/L) and grade 2 (serum phosphorus < 0.61 mmol/L) hypophosphataemia during follow-up, respectively. Conclusions Although slight increases in SCr did occur after starting TDF, clinically significant nephrotoxicity was rare. The clinical significance of TDF-related hypophosphataemia and proteinuria requires further study.