1. The major metabolite of 2,4-dimethoxy-6-sulphanilamidopyrimidine (sulphadimethoxine) in urine in man is a non-reducing glucuronide, which has been isolated and characterized as its S-benzylthiouronium salt. 2. The same compound was made synthetically by standard methods from sodium sulphadimethoxine and methyl 2,3,4-tri-O-acetyl-1-bromoglucuronate. 3. On hydrolysis with acid, the glucuronide yielded sulphanilic acid, glucuronic acid and barbituric acid, and with beta-glucuronidase it slowly yielded sulphadimethoxine and glucuronic acid. 4. Evidence based on infrared spectra and other data showed that the urinary and synthetic glucuronide was 1-deoxy-1-[N(1)'-(2'',4''-dimethoxypyrimidin-6'' -yl)sulphanilamido-beta-d-glucosid]uronic acid or sulphadimethoxine N(1)-glucuronide. 5. N(1)-Methyl- and N(ring)-methyl derivatives of sulphadimethoxine and 4-methoxy-6-sulphanilamidopyrimidine were prepared and their infrared and ultraviolet spectra determined for comparison.

1. The fate of sulphadimethoxine (2,4-dimethoxy-6-sulphanilamidopyrimidine) was studied in man, rhesus monkey, dog, rat, guinea pig and rabbit. 2. About 20-46% of the dose (0.1g./kg.) of the drug is excreted in the urine in 24hr. in these species, except the rat, in which only 13% is excreted. 3. In man and the monkey sulphadimethoxine N(1)-glucuronide is the major metabolite in the urine. In the rabbit and guinea pig N(4)-acetylsulphadimethoxine is the main metabolite. In the dog the drug is excreted mainly unchanged. In the rat equal amounts of the unchanged drug and its N(4)-acetyl derivative are the main products. 4. Small amounts of sulphadimethoxine N(4)-glucuronide are found in the urine of all the species. Sulphadimethoxine N(1)-glucuronide occurs in small amounts in the urine of rat, dog and guinea pig; none is found in rabbit urine. 5. Sulphadimethoxine N(4)-sulphate was synthesized and found to occur in small amounts in rat urine. 6. Monkey liver homogenates fortified with UDP-glucuronic acid are able to synthesize sulphadimethoxine N(1)-glucuronide with the drug as substrate. Rat liver has also this ability to a slight extent, but rabbit liver is unable to do so. 7. Sulphadimethoxine N(4)-glucuronide is formed spontaneously when the drug is added to human urine. 8. The biliary excretion of the drug and its metabolites was examined in rats. The drug is excreted in rat bile mainly as the N(1)-glucuronide. The N(1)- and N(4)-glucuronides administered as such are extensively excreted in the bile by rats.

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The fate of orally administered ethionamide (2‐ethyl‐4‐thiocarbamoylpyridine) and ethionamide sulphoxide in man, rats, mice and dogs has been examined. Though spontaneous interconversion between the two antituberculosis drugs does not take place, there was extensive interconversion in vivo, both appearing in the blood within 15 min of dosing irrespective of which compound was administered. Species differences were evident in both the rate of metabolism and in the ethionamide: ethionamide sulphoxide ratio. Apart from this interconversion, ten probable urinary metabolites were detected. These consisted of six fluorescent and four non‐fluorescent metabolites, three of the latter being identified as 2‐ethylisonicotinamide, 2‐ethylisonicotinic acid and inorganic sulphate. A scheme is proposed to cover part of the common metabolic route of the two drugs.