RESUMO
Aim: The application of factorial experimental design to evaluate the effect of particle size, capsule surface coating and binder concentration on the in vitro controlled release profile of metronidazole from encapsulated granules. Methodology: Metronidazole granules were prepared by the wet granulation technique and encapsulated in hard gelatin capsule shells. Eudragit® L-100 and Landolphia owariensis latex served as primary and secondary coatings respectively on 50 or 75% of capsule surface. The three formulation factors (% capsule surface coating, matrix former concentration and particle size) were subjected to a 2x3x4 factorial design experiment using the software (JMP 4.0.4, SAS Inc. USA). Gradient drug release studies were conducted in three media; firstly in media of pH 1.2 for 2 h, pH 6.8 for 3 h and finally pH 7.4 until exhaustion of drug release. The drug release data were subjected to kinetic treatment to establish operational release kinetics such as zero order, first order, Higuchi, Hixon Crowell and Kitazawa, while the power law enabled the prediction of mechanism of drug release. Results: Results showed that % capsule surface coated with Landolphia owariensis latex and particle size significantly (p<0.05) contributed to time of drug release (T7.4) at pH 7.4. In tandem with this, maximum amount of drug released (D7.4) at pH 7.4 was significantly (p<0.05) affected by particle size alone. A few batches were characterized by anomalous transport while over 80% were associated with super case 11 type of release. Conclusion: We therefore conclude that, factorial experimental design identified Landolphia owariensis latex coating and particle size of granules as being chiefly responsible for drug release variations.