Weight-based tacrolimus trough concentrations post liver transplant

Tacrolimus is one of the most widely used liver transplant medications. With the increasing number of obese patients requiring liver transplants, knowledge of the effect of body size affecting post-transplant outcomes, for example drug exposure is increasingly required.

(i) To investigate whether patient body size (i.e. total bodyweight) affects trough plasma concentrations of tacrolimus when a standard mg/kg dosing regimen is used; and (ii) to investigate whether obese patients have different numbers of plasma concentrations outside the therapeutic range compared to non-obese patients in the first months after liver transplant.

Using a transplant database, data tacrolimus concentrations were available for 69 patients. Tacrolimus was initially dosed at a standard 0.1 mg/kg/day after liver transplant, and adjusted to maintain a target trough concentration. Trough blood samples, phenotypic and outcome variables were analysed.

Trough concentrations were similar between obese and non-obese patients (P > 0.05) at each sampling day. At day 7 post-transplant, 85.7% and 79.5% of the observed plasma concentrations were outside the recommended therapeutic range for obese and non-obese patients respectively, at day 30, 52.9% and 57.4%, and at 6 months, 18.7% and 27.5%.

In the first week post-transplant, tacrolimus trough concentrations after standard mg/kg dosing post liver transplant appear to be corrected by total bodyweight. Obese patients have a similar number of trough plasma concentrations outside the therapeutic range compared to non-obese patients.