A colorimetric procedure is described for the microdetermination of meprobamate in biological fluids. Meprobamate is extracted from plasma or serum using mixed chloroform-carbon tetrachloride solvent, and color development is effected by treatment with p-dimethylaminobenzaldehyde and antimony trichloride in acetic anhydride. The color intensity measured at 5 5 0 mp is pro ortional to the concentration over the range of 0.5 to 10 mcg. A suitable modigation of the extraction procedure for use with urine specimens is also described, which permits separation of meprobamate from the higher concentration of endogenous interfering substances present in urine. Determination of meprobamate concentrations in blood specimens from normal adult subjects indicates that a peak concentration of this drug is attained about two hours after oral administration.
N EARLIER PUBLICATIONS (1-7) it h a been shown that orally administered meprobamate is readily absorbed into the blood stream from the gastrointestinal tract of experimental animals and of humans and is excreted in the urine in an unchanged form, as a hydroxylated derivative, and in the form of a yet unidentified glucuronide. The analytical methods used in connection with these studies generally employed nonspecific colorimetric procedures or depended solely or partly on chromatographic separation. In some animal studies CI4-labeled meprobamate was utilized as a basis for analysis. None of the published methods permits a rapid and practical estimate of meprobamate content in blood and urine in the concentrations normally encountered and in the presence of endogenous interfering substances.
Ludwig and Hoffman (8) described a chemical reaction between meprobamate and certain aldehydes which served as a basis for a colorimetric procedure for the determination of this drug. I t is the purpose of this publication to present a simplified and improved modification of this highly specific method and to show its application to a series of blood concentration and urinary excretion studies conducted on adult human subjects.
Meprobamate develops an intense red-violet color when reacted with certain aldehydes and anhydrous metallic salts in the presence of acid dehydrating agents.' An examination of the action of a number of such combinations led to the selection of 9-dimethylaminobenzaldehyde and antimony trichloride in acetic anhydride as the re-*