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

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Abstract
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 μmol/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 μmol/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.