Coadministration of tenofovir decreased atazanavir plasma concentration after unilateral nephrectomy

We report a case in which the atazanavir (ATV) concentration in the plasma decreased after unilateral nephrectomy in a patient receiving tenofovir (TDF). The patient was a 39-year-old man diagnosed with human immunodeficiency virus type 1 infection and was being treated with TDF/emtricitabine, ATV, and ritonavir. Before nephrectomy, ATV and TDF plasma trough concentrations were 810 and 65 ng/ml, respectively. At this time, estimated glomerular filtration rate (eGFR) was 111 ml/min/1.73 m2. Approximately 5 months after starting antiretroviral therapy (ART), the patient underwent nephrectomy. Plasma concentrations were remeasured 18 weeks after the operation, and the TDF concentration had increased to 109 ng/ml, whereas the ATV concentration decreased to 290 ng/ml. His eGFR decreased to 50 ml/min/1.73 m2 at the time of the second measurement. The decreased ATV plasma concentration suggested that interactions between ATV and TDF were exacerbated by an increase in TDF plasma concentration caused by renal dysfunction. This case report suggests that it is important to monitor the ATV plasma concentration to ensure that it is no less than the target trough concentration when renal function decline is observed in patients receiving ART including ATV and TDF.