Pharmacokinetic Study of a Soft Gelatin Capsule and a Solid-Supersaturatable SMEDDS Tablet of Dutasteride in Beagle Dogs

Dutasteride, an analog of testosterone, a 5α-reductase inhibitor is widely used in the treatment of moderate to severe symptomatic benign prostatic hyperplasia. The aim of this study was to compare the pharmacokinetic characteristics of dutasteride in beagle dogs after oral administration of a conventional soft gelatin capsule (Avodart®) and a novel solid-supersaturatable soft-microemulsifying drug delivery system (SMEDDS) tablet. In this comparative dissolution study, the dissolution of dutasteride was pH-independent for both formulations. Noncompartmental analysis and modeling approaches were carried out to determine the pharmacokinetic parameters of dutasteride. Approximately 90% of the drug dissolved in all media within 15 min, indicating that there was little difference in the dissolution rate of the solid-supersaturatable SMEDDS tablets and that of the commercial soft gelatin capsules. Using t test analysis, no statistically significant difference was detected in the pharmacokinetic parameters of the two formulations. The test/reference geometric mean ratios were 1.087 (90% confidence intervals 0.8529–1.3854) for the area under the plasma concentration versus time curve from 0 to the last time point (48 h) with a measurable concentration and 1.094 (90% confidence intervals 0.8909–1.3454) for maximum plasma concentration. Unfortunately, the bioequivalent criterium (0.8–1.25) was not met due to the small sample size, but the results of this study suggest a possible bioequivalence of dutasteride in the two formulations. Based on the results of this study, the development of a tablet dosage form of dutasteride using a solid-supersaturatable SMEDDS should be considered for humans.