Once- versus twice-daily tacrolimus: are the formulations truly equivalent?

Tacrolimus is a cornerstone immunosuppressant agent in the prevention of organ rejection following transplantation. While typically administered twice daily (Prograf®), a modified-release once-daily formulation (Advagraf®) has recently been developed and licensed for use. To date, the majority of published data relating to the use of Advagraf® have arisen from industry-sponsored clinical trials. These have shown that conversion from Prograf® to Advagraf® on a 1 mg : 1 mg basis in both stable and de novo kidney and liver transplant recipients yields lower peak concentrations (C(max)) but equivalent overall drug exposure (area under the concentration-time curve from 0 to 24 hours post-dose; AUC(24)) and trough concentrations (C(min)). This has led to the proposal that the same total daily dose, target C(min) and therapeutic drug monitoring (TDM) strategies can be applied irrespective of preparation. However, while Advagraf® fulfils criteria for bioequivalence according to the European Medicines Agency and US FDA, lower tacrolimus exposure has been observed in the majority of clinical studies, particularly in the early post-transplant period. This has resulted in a need for higher doses of Advagraf® compared with Prograf® to achieve similar C(min) values. Significant between-subject variability in the C(min)/AUC(24) relationship with Advagraf® has also been demonstrated, suggesting possible problems with TDM based on C(min) values. In non-comparative conversion studies, Advagraf® demonstrated similar efficacy and safety to Prograf®. However, phase III studies in de novo kidney and liver transplant recipients have shown higher rates of acute rejection with Advagraf®, possibly explained by the differing C(max) values achieved with the two preparations. While it has been suggested that once-daily administration may improve compliance, no studies have proven this to be the case. This article reviews the pharmacokinetics, efficacy, adverse effects and utility of Advagraf® in relation to its equivalence to Prograf®, and areas that require additional research are identified.