The absorption kinetics of different pharmaceutical formulations of orally and rectally administered flecainide have been assessed in a cross-over study in 7 healthy volunteers. The subjects received single doses of flecainide after a washout period of at least one week. A tablet, an oral solution, a rectal solution and a 10 min i.v. infusion during 10 min each containing 100 mg flecainide were administered to the subjects in a randomized order.
The mean absolute bioavailability was 98%, 78% and 81% for the rectal and oral solutions and the tablet. The lag time after administration of the oral solution was 0.33 h and it was 0.86 h after the tablet and 0.18 h after the rectal solution. The mean time to the peak serum concentration (tmax) after the rectal solution (0.67 h) was shorter than after either the tablet (4 h) or oral solution (1 h). The maximum serum concentration (Cmax) was 0.29 mg · 1−1 after the rectal solution, 0.14 mg · 1−1 after the tablet and 0.17 mg · 1−1 after the oral solution. All the volunteers showed significantly higher serum flecainide concentrations during the first 20 min of the absorption phase after rectal administration of 100 mg flecainide as a solution compared to its oral administration.
In conclusion: based on the absolute bioavailability, Cmax, tmax, and lag times, rectal administration of flecainide solution gave a better absorption profile than after oral tablet or solution.