Assessment and Monitoring of Renal Proximal Tubular Tolerance of Nucleoside and Nucleotide Analogues Using Early Screening Tools in Patients Chronically Mono-infected With Hepatitis B Virus

Overview

Nucleotide analogues are associated in the long term with a risk of proximal tubular nephropathy (PT) with loss of phosphate, and, when compensatory mechanisms are overwhelmed, with osteopenia or osteoporosis. This toxicity has been particularly documented for tenofovir (TDF) in HIV disease, but its prevalence varies widely in the literature and is mainly associated with comorbidities: on average this prevalence is 0.39% after 48 weeks with exceptional cases of Fanconi syndrome described. In HBV monoinfection after 60 months of treatment with TDF, an 11% decrease of creatinine clearance (CreatCl) is observed. A single study showed a significant increase in creatinine level with entecavir (ETV) therapy, a second-generation nucleoside, hitherto not described as nephrotoxic. Furthermore, if the direct renal toxic effect characteristic of HIV in the kidney is well known, the role of HBV is less clear. Thus, HBV treatment appears to have a renal protective effect. The monitoring tools recommended by the SPC, CreatCl and plasma phosphorus level are late markers of tubular damage. The threshold of phosphate tubular reabsorption (TmPi/GFR) and the fractional excretion of uric acid (FEUA) are unexpensive early screening tools. However, the long-term evolution of this subclinical tubular involvement in HBV monoinfection is not known.

260 naive untreated patients, 220 patients treated with TDF and 220 patients treated with ETV and consecutively recruited in this interventional study, will have at baseline and every three months, a determination of phosphorus, creatinine, uric acid in plasma and urine samples for determination of TMPi / GFR and FEUA, and an evaluation of urinary calcium level. Depending on local opportunities, every six months, a urine sample will be stored in a declared biological collection to perform β2-microglobuline and cystatin dosage. A 25-OHD3 and PTH dosage will be conducted annually. A sample of genomic DNA will be collected after informed consent of the patient from a saliva sample (Saliva autocollection kits) in order to investigate genetic polymorphism in transporters responsible for the renal elimination of TDF and ETV. A serum sample will be stored at baseline, at one year and at endpoint for the retrospective dosage of bone markers (bone PAlk, PINP and CTX).