A simple method is described for the determination of antihistamines in commercially produced tablets and capsules. It consists of extraction of the antihistamine from the pharmaceutical product with chloroform and visual titration of the extract with perchloric acid titrant, after the addition of acetic acid or acetonitrile and a suitable indicator. Most excipients are insoluble in chloroform while still others are not titrated under the conditions of the analysis. The method is rapid and applicable to all but a few of the products tested.
EVERAL WORKERS have attempted to develop S a general procedure for the determination of antihistamines. Bandelin, et al.
(1), analyzed ten antihistamines colorimetrically, using ammonium reineckate reagent and applied the method with success to five commercial samples of the tablets and capsules as well as to other pharmaceutical products. Blaug and Zopf (2) determined ten pure antihistamine salts using ion exchange and utilized this method successfully in the analysis of tripelennamine hydrochloride in various pharmaceuticals. Rasmussen, et al.
(3), prepared the picrates of twenty antihistamines and determined their equivalent weights by potentiometric titration in 1 to 1 glacial acetic acid chloroform solution, although this method was not recommended for the quantitative determination of these compounds in commercial products. Other methods have been published for the analysis of antihistamines but for the most part these apply to a single compound (4), or to a limited group of compounds, such as the Konig reaction ( 5 ) , specific for compounds with a 2-pyridyl group or the method of Heim (6), which is applied to antihistamines containing an ether group. Spectrophotometric procedures have been most widely adopted as official methods for determining antihistamines in pharmaceutical preparations, while nonaqueous titrations in glacial acetic acid have been chosen generally for the analysis of the pure compounds 8). Kleck-