A new microemulsion formulation of cyclosporin: pharmacokinetic and clinical features

Cyclosporin (cyclosporin A) has been used as an immunosuppressive agent after organ transplantation for more than 15 years. The bioavailability of cyclosporin in its conventional oral formulation 'Sandimmun' displays considerable inter- and intra-patient variability. Absorption is also bile dependent. Recently, a new galenic formulation of cyclosporin was introduced, 'Neoral', which is a water-free microemulsion of cyclosporin. The microemulsion creates micelles which are absorbed in the small bowel without the presence of bile. Pharmacokinetic studies in healthy volunteers clearly demonstrate an increased bioavailability of the microemulsion formulation of cyclosporin, measured as an increase in maximum drug concentration (Cmax) and area under the drug concentration-time curve, and a reduced time to Cmax. These findings have been confirmed in kidney, liver and heart transplant recipients. With the microemulsion formulation, an improved prediction of cyclosporin concentrations has probably attributed to the decrease found in the variability of cyclosporin absorption. This could probably enable easier and more reliable monitoring of cyclosporin concentrations after transplantation. So far, data on the effects of conversion from the conventional to the microemulsion formulation of cyclosporin are only available in a limited number of patients and with a limited follow-up period. The main questions are related to what the long term consequences of the improved bioavailability of the microemulsion formulation will be. Further long term studies are needed in order to answer these questions. In the present review, we report on the pharmacokinetic properties of, and on clinical experience after solid organ and bone marrow transplantation with, the microemulsion formulation.