THE DETERMINATION OF PROBENECID (BENEMID) IN BODY FLUIDS

¹ Pharmacology Section, Sharp & Dohme Division, Merck & Co., Inc., West Point, Pa.

Two analytical methods for the determination of Benemid in body fluids have been described. The spectrophotometric procedure, recommended for carefully controlled experimental work, depends upon the fact that the compound can be extracted into chloroform from an acidic, aqueous medium and in turn reextracted into 0.1 N NaOH. The alkaline solution is examined spectrophotometrically at a wave length of 242.5 mµ.

In the second method the drug is also extracted into chloroform from an acidic, aqueous medium. The chloroform layer is shaken with an aqueous solution of methylene blue. The colored salt formed at the interface is soluble in the solvent, making it possible to determine the amount present by examining the chloroform layer colorimetrically. This procedure is the method of choice for clinical studies, since it is unaffected by most medicaments and endogenous metabolic products.

The experiments presented herein indicate that Benemid is well absorbed following oral administration, that a considerable amount is adsorbed on plasma protein (albumin), and that the adsorption curve corresponds to a physical adsorption isotherm. Evidence has also been given for the appearance of one and probably two hydrolyzable metabolites in the urine of dogs that have received repeated large doses of Benemid.