Oral iloprost in healthy volunteers

Iloprost is a potent chemically stable PGI2-mimetic. Therapeutic efficacy was shown after i.v. infusion treatment in several states of peripheral vascular disease. For out-patient therapy an oral dosage form should be developed. Based upon dissolution profiles and in vivo data of a pig model, three different film-coated pellet formulations were selected for pharmacokinetic characterization in nine healthy volunteers. In the first part of the study groups of three test subjects were treated with increasing dosages (150-300 micrograms) of iloprost. At 300 micrograms flush and headache led to the discontinuation of those titration. All formulations exhibited dose-dependent serum level profiles. The cross-over characterization in all test subjects showed that one formulation, which exhibited a modified in vitro dissolution of 60% of the dose within 1 h in pH 7.4 phosphate buffer, was optimal from the pharmacokinetic profile. After oral administration of this formulation the bioavailable dose fraction was highest and half-maximal serum levels lasted for 2.4 h (mean); therapeutic serum levels were maintained for 2.1-5.0 h. This formulation was chosen for further investigation to imitate therapeutic serum level profiles as obtained after i.v. infusion for 4-6 h with a once-a-day dosage form.