Identification of drugs in pharmaceutical dosage forms by X-ray powder diffractometry.

A simple X-ray powder diffractometric (XRD) method was developed for the identification of the active ingredient in a variety of dosage forms. The method was successfully used to unambiguously identify the active ingredient(s) in tablet, capsule, suppository and ointment formulations. The unique feature of the method is that it provides information about the solid-state of the drug. Thus, a capsule formulation containing anhydrous ampicillin was readily distinguished from that containing ampicillin trihydrate. The USP stipulates the use of the beta-polymorphic form of anhydrous carbamazepine in carbamazepine tablets. Contamination by the alpha-polymorph (down to a level of 1.4% w/w of the formulation) could be detected. In some of the multicomponent formulations, there was a pronounced overlap of the powder patterns of ingredients which made identification difficult. This problem was solved by using a pattern subtraction technique, which permitted selective subtraction of the XRD pattern of the constituents of the formulation from the overall XRD pattern. Such an approach enabled identification of the drug even when it constituted only 5% w/w of the formulation. The method also permitted simultaneous identification of the multiple active ingredients in trimethoprim-sulfamethoxazole and acetaminophen-aspirin-caffeine formulations.