Apparent low absorbers of cyclosporine microemulsion have higher requirements for tacrolimus in renal transplantation

Bioavailability and exposure of cyclosporine microemulsion and tacrolimus in renal transplantation are governed by many complex factors. Failure to achieve therapeutic two-h post-dose (C-2) levels despite adequate doses of cyclosporine ("low absorbers") may merit conversion to tacrolimus. We compared tacrolimus dose requirements in "low absorbers" (n = 15) with a random control group of de novo tacrolimus patients (n = 14). Low absorbers failed to reach target C-2 despite increasing dose from 10.1 to 16.2 mg/kg/d. At conversion the mean C-2 was 969 ng/mL (95% Cl: 684-1255; target 1700 ng/mL). Low absorbers tended to be younger, heavier, and diabetic. Despite a similar initial tacrolimus dose (0.17-0.18 mg/kg/d), low absorbers required a much higher daily dose to achieve target; 0.25 vs. 0.16 mg/kg/d (p = 0.016). Furthermore, daily maintenance tacrolimus remained much higher in low absorbers at three wk (0.22 vs. 0.13 mg/kg/d, p = 0.012). Although not statistically significant, this group experienced an acute rejection rate of 33%, compared with 21% in the control group. Patients treated with cyclosporine as initial immunosuppression who fail to reach target C-2 levels in a timely fashion are at risk for impaired bioavailability of tacrolimus. Based on our data, a starting dose of 0.25 mg/kg/d in divided doses may be warranted for low absorbers converting to tacrolimus; however, we encourage larger studies with formal pharmacokinetic analysis in this population.