Formulation Development of Morphine Sulfate Sustained-Release Tablets and Its Bioequivalence Study in Healthy Thai Volunteers

The objectives of this study were to develop morphine sulfate sustained-release tablet formulations and to evaluate the bioequivalence compared with a commercial brand. The physicochemical properties of the formulated and commercial tablets were determined and compared. The bioequivalence investigation was carried out in 15 healthy male volunteers who received a single dose in a randomized two-way crossover design. After dosing, serial blood samples were collected for a period of 24 h. Morphine concentration was assayed by high-performance liquid chromatography with electrochemical detector. The log-transformed Cmax and AUCs were statistically compared by analysis of variance, and the 90% confidence intervals (CIs) of the ratio of the log-transformed Cmax and AUCs between the most promising developed formulation and the commercial product were determined. It was found that the dissolution rate profile of a developed formulation was similar to the commercial brand. Their similarity and difference factors were well within limits. In the bioequivalence study, the AUClast and AUCinf between the test and the reference products were not statistically different (p = 0.227 and p = 0.468, respectively), with the 90% CIs of 83.4–102.6% and 87.7–139.4%, respectively. However, the Cmax of the two formulations was significantly different (p = 0.019). The 90% CI of the developed formulation was 72.0–93.0% compared to the commercial product. In vitro dissolution of locally prepared morphine sulfate sustained-release tablets was comparable to commercial brand. However, the results justified the conclusion of lack of bioequivalence of the developed product to the commercial one.