Development and validation of three stability-indicating methods for determination of bisacodyl in pure form and pharmaceutical preparations

Three new, simple, sensitive, and accurate stability-indicating methods were developed for quantitative determination of bisacodyl in the presence of its degradation products, monoacetyl bisacodyl (I) and desacetyl bisacodyl (II), in enteric coated tablets, suppositories, and raw material. The first is a spectrodensitometric method in which the drug is separated from I and II on silica gel plates using chloroform-acetone (9 + 1, v/v) as the mobile phase with ultraviolet detection of the separated bands at 223 nm over a concentration range of 0.2-1.4 mu g/band for bisacodyl with mean recovery 100.35 +/- 1.923%. The second method is fourth derivative D-4 spectrophotometry, which allows determination of bisacodyl in the presence of its degradation products in raw material at 223 nm using acetonitrile as the solvent with adherence to Beer's law over the concentration range 2-18 mu g/ml with mean recovery 99.77 +/- 1.056%. In the third method, the spectrophotometric data of bisacodyl, I, and II using absolute ethanol as solvent were processed by 3 chemometric techniques: classical least-squares, principal component regression, and partial least-squares. A training set consisting of 15 mixtures containing different ratios of bisacodyl, I, and II was used for construction of the 3 models. A validation set consisting of 6 mixtures was used to validate the prediction ability of the suggested models. The 3 chemometric methods were applicable over a concentration range between 2-14 mu g/mL for bisacodyl with mean recovery of 99.97 +/- 0.865, 100.01 +/- 0.749, and 99.97 +/- 0.616% for the 3 models, respectively. The proposed methods were checked using laboratory-prepared mixtures and were successfully applied to the analysis of raw material and pharmaceutical formulations containing bisacodyl, except for the second method that applies only for raw material. The validity of the suggested procedures was further assessed by applying the standard addition technique; the recoveries obtained were in accordance with those given by the reference method.