Surfactant effects upon dissolution patterns of carbamazepine immediate release tablet

The objective of this study was to investigate the effects of sodium lauryl sulfate upon the saturation solubility of carbamazepine, its dissolution kinetics, and T_50% defined as the time required for dissolving 50% of carbamazepine. Water, 0.1N-HCl, and phosphate buffers at pH 4.0 and 6.8 containing 0.1, 0.5, 1, and 2% sodium lauryl sulfate were used as dissolution media. The dissolution study was conducted by using the USP dissolution apparatus II with an agitation rate of 75 rpm. Samples of the dissolution media were taken in 7, 15, 30, 45, 60, 75, and 90 min, and the amounts of carbamazepine were determined spectrophotometrically at 285 nm. All dissolution data were fitted well into a four-parameter exponential equation: Q = a(1 - e^-bxt) + c(1 - e^-dxt). In this equation Q represented % carbamazepine dissolved at a time t, and a, b, c, and d were constants. This equation led to the calculation of dissolution rates at various time points and T_50%. It was found that the dissolution rate of carbamazepine was directly proportional to the aqueous concentration of sodium lauryl sulfate. In addition, under our experimental conditions T_50% values ranged from 37.8 to 4.9 min. It was interesting to note that T_50% declined rapidly as the surfactant concentration increased from 0.1 to 0.5%, whereas it declined more slowly at concentrations greater than 1%. These results clearly demonstrated that the dissolution rate of carbamazepine and duration of its dissolution test could be tailored by optimizing the amount of sodium lauryl sulfate in a dissolution medium.