Pharmacokinetics of low-dose cidofovir in kidney transplant recipients with BK virus infection.

BACKGROUND: BK virus (BKV) infection in kidney transplant recipients is associated with progressive graft dysfunction and graft loss. Cidofovir, an antiviral agent with known nephrotoxicity, has been used in low doses to treat BKV infections. However, the systemic exposure and disposition of the low-dose cidofovir regimen are not known in kidney transplant recipients. METHODS: We investigated the pharmacokinetics (PK) of low-dose cidofovir (0.24 - 0.62 mg/kg) both without and with oral probenecid in 9 transplant patients with persistent BK viremia without nephropathy in a crossover design. RESULTS: The mean estimated glomerular filtration rate (eGFR) of the study participants was 46.2 mL/min/1.73 m(2) (range: 17-75 mL/min/1.73 m(2) ). The contribution of active renal secretion to cidofovir total body clearance was assessed by evaluating the effect of probenecid on cidofovir PK. Maximum cidofovir plasma concentrations, which averaged approximately 1 µg/mL, were significantly below the 36 µg/mL 50% effective concentration in vitro for cidofovir against BKV. The plasma concentration of cidofovir declined with an overall disposition half-life of 5.1 ± 3.5 and 5.3 ± 2.9 h in the absence and in the presence of probenecid, respectively (P > 0.05). CONCLUSIONS: Cidofovir clearance and eGFR were linearly related irrespective of probenecid administration (r(2) = 0.8 without probenecid; r(2) = 0.7 with probenecid). This relationship allows for the prediction of systemic cidofovir exposure in individual patients and may be utilized to evaluate exposure-response relationships to optimize the cidofovir dosing regimen for BKV infection.

The impact of conversion from prograf to generic tacrolimus in liver and kidney transplant recipients with stable graft function.

Bioequivalence of the recently available generic tacrolimus formulation, manufactured by Sandoz, to the reference product (Prograf; Astellas Pharma, Tokyo, Japan) has been demonstrated in healthy subjects. However, the safety and efficacy of substitution with generic tacrolimus in transplant patients have not been evaluated. Tacrolimus trough concentrations and indices of liver and kidney function were recorded before and after generic substitution in 48 liver and 55 kidney transplant recipients. In liver transplant patients, the mean tacrolimus concentration/dose (C/D) ratio (± SD) was 184.1 (± 123.2) ([ng/mL]/[mg/kg/day]) for the reference product and 154.7 (± 87.8) ([ng/mL]/[mg/kg/day]) for the generic product (p < 0.05). The mean C/D-ratios in kidney transplant patients were 125.3 (± 92.7) and 110.4 (± 79.2) ([ng/mL]/[mg/kg/day]) for the reference and generic products, respectively (p < 0.05). Actual trough concentrations declined by an average of 1.98 ng/mL in liver and 0.87 ng/mL in kidney transplant patients following the switch, after accounting for all significant covariates. No change was observed in biochemical indices of liver or kidney function and no cases of acute rejection occurred following the substitution. These results suggest that transplant patients currently taking the reference tacrolimus formulation may be safely switched to the Sandoz-generic product provided trough concentrations are closely monitored following the substitution.