Relative bioavailability of cyclosporin from conventional and microemulsion formulations in heart-lung transplant candidates with cystic fibrosis

Patients with cystic fibrosis absorb cyclosporin poorly and erratically. We have compared the relative bioavailability of cyclosporin from conventional and microemulsion formulations in 5 adult heart-lung transplant candidates with cystic fibrosis. Relative bioavailability was compared at two dose levels (200 mg and 800 mg). A randomized 4-period cross-over study was performed with at least a 7 days washout period between each single dose pharmacokinetic study. Blood cyclosporin concentrations were measured by a selective monoclonal antibody-based radioimmunoassay. The bioavailability of cyclosporin from the microemulsion formulation was 1.84 (95% C.I. 1.05 to 3.22; P–0.04) and 2.09 (95% C.I. 0.95 to 4.61; P–0.06) times higher compared with the conventional formulation at 200 mg and 800 mg respectively. C_max following the microemulsion formulation was 3.38 (C.I. 1.14 to 10.59; P–0.04) and 2.77 (C.I. 1.48 to 5.19; P–0.01) times higher compared with the conventional formulation at 200 mg and 800 mg respectively. The higher C_max following the microemulsion formulation was accompanied by shorter t_max. An enhancement of cyclosporin absorption with the microemulsion formulation was demonstrated in each patient for at least one dose level. We conclude that rate and extent of cyclosporin absorption from the microemulsion formulation is greater compared with the conventional formulation in patients with cystic fibrosis. The potential therapeutic and economic benefits of the micro-emulsion formulation should be evaluated in cystic fibrosis patients following heart-lung transplantation.