Quantitative determination of four antihistamines in combination by high-pressure liquid chromatography.

A procedure used to assay four antihistamines--brompheniramine maleate, chlorpheniramine maleate, pheniramine maleate and pyrilamine maleate in combination--is discussed. The method requires a high-pressure liquid chromatograph and an intermediate polarity column. The method is accurate and appears to be stability-indicating. The four antihistamines can be separated and assayed accurately. There is no interference from the two commonly used decongestants, phenylephrine hydrochloride and phenylpropanolamine hydrochloride, from the expectorant potassium guaiacolsulfonate, from the preservative propyl paraben or from two other antihistamines, diphenhydramine hydrochloride and bromdiphenhydramine hydrochloride. Guaifenesin, methylparaben and sodium benzoate interfere only with pheniramine maleate. Methapyrilene hydrochloride interferes only with pyrilamine maleate.