A new spectrophotometric method for the quantitative determination of Metopimazine based on the absorbance of its sulfoxide

Metopimazine (MPZ) is a dopamine antagonist from the phenothiazine class of drugs. It has antiemetic properties and is used to treat nausea and vomiting, including those associated with cancer chemotherapy. We have proposed a new method for the quantitative determination of Metopimazine by spectrophotometry. The drug is determined using a difference spectrophotometric technique based on the absorbance of its previously prepared sulfoxide derivative (lambda(max) = 355 nm, epsilon = 4.5 x 10(3) L/mol cm) relative to a solution of a non-derivatised drug. The sulfoxide derivative is formed quickly and quantitatively at room temperature by adding potassium caroate solution. The difference in the absorbance of solutions at 355 nm is proportional to the concentration of MPZ in the drug. The method is specific for an intact drug in the presence of oxidative and photochemical decomposition products and excipients. The linearity range is 0.9-30.0 mu g/mL. Regression line equation: Delta A = 0.0061 x c (r = 0.999), where c is the MPZ concentration in mu g/mL. The limit of quantitation, LOQ (10S), is 2.8 mu g/mL. The possibility of quantitative determination of MPZ content in the bulk drug and tablets of Vogalen Lyok 7.5 mg with a relative standard deviation of 1.21% (delta = + 0.05%) and 1.38% (delta = - 0.67%), respectively, was shown. |delta| < t(alpha) (0.95, n = 7) x RSD/root n, where delta = (<(x)over bar>-mu) x 100%/mu (mu-quantification data, given in the Certificate of Quality).