Relative Bioavailability of an Extemporaneous Ondansetron 4-mg Capsule Formulation versus Solution

Study Objective. To compare the relative bioavailability of an extemporaneous ondansetron capsule formulation with that of an identical dose of the commercially available solution formulation. Design. Open-label, randomized, two-way crossover study. Setting. University-affiliated research laboratory. Subjects. Sixteen (eight men, eight women) healthy, nonsmoking volunteers. Intervention. Participants were randomly assigned to receive a 4-mg dose of either the commercially available ondansetron solution or the extemporaneous ondansetron capsule formulation. Blood sampling was performed over 12 hours after dosing. After a washout period of at least 3 days, each participant was switched to the alternate formulation, and blood sampling was repeated. Measurements and Main Results. Ondansetron was well absorbed after administration of both formulations, with the solution achieving a faster rate of drug absorption over the first hour of dosing. After the peak plasma concentration was achieved, the plasma concentration-time curves of both formulations declined at a similar steady rate. There were no significant differences in pharmacokinetic parameters between the two formulations, and the relative bioavailability of the capsule versus the solution formulation was 101%. Conclusions. Similar concentration-time curves and pharmacokinetic parameters were achieved with the two formulations. The commercially available solution would be a useful alternative formulation for administration of low-dose ondansetron in research and clinical settings.