Two simple and selective spectrophotometric methods are described for the determination of isoxsuprine hydrochloride (ISX.HCl) as base form in bulk drug and in injections and tablets. The methods are based on the molecular charge-transfer complexation of ISX base (ISX) with either p-chloranilic acid (PCA) or 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The intense colored radical anions formed on dissociation, are quantitated at 520 nm (PCA method) or 600 nm (DDQ method). The optimum assay conditions were optimized. Beer's law is obeyed in the concentration ranges 5.28 x 10(-5) to 42.2 x 10(-5) mol dm(-3) in PCA method and 0.79 x 10(-5) to 10.6 x 10(-5) mol dm(-3) in DDQ method, with respective molar absorptivity values of 1.32 x 10(3) and 6.55 x 10(3) dm(3) mol(-1) cm(-1). The reaction stoichiometry in both methods was evaluated by either Job's method or limiting logarithmic method and was found to be I:I (ISX: PCA, ISX: DDQ). Developed methods were validated according to ICH guidelines and found to be accurate and precise
