The metabolism of sulphonamides: 3. The detection of 3-hydroxysulphanilamide in the urine of hospital patients treated with sulphanilamide

Pharmacokinetics of sulphanilamide and its three acetyl metabolites in dairy cows and calves

An intravenous low dosage of sulphanilamide (SAA) (14.0 mg/kg) to 6 pre-ruminant calves revealed a biphasic SAA plasma disposition with a mean elimination half-life of 4.1 h. The main metabolite in plasma was N4-acetylsulphanilamide (N4), which 4 hours after injection exceeded the parent SAA plasma concentration. Urinary recovery of SAA was 10 to 16% of the dose; of N4, it was at least 69%. Traces of the N1-acetyl (N1) metabolite and the doubly acetylated derivative (N1N4) were present in urine. The renal clearances of the N1 and N4 metabolites showed a tubular secretion pattern, which was at least 2 to 6 times higher than that of SAA. A single high oral SAA dose of 200 mg/kg to 3 dairy cows resulted in extensive metabolism of SAA into N4, N1, and N1N4 metabolites; their mean maximum plasma concentrations were 64, 48, 0.72 and 24 micrograms/ml, respectively. The mean disposition half-life of SAA in plasma and milk was 10 h. In milk the metabolite concentrations exceeded those in plasma; the N4 and N1N4 metabolite concentrations in milk exceeded that of SAA. The mean maximum concentrations of SAA, N4, N1, and N1N4 in milk were 52, 89, 2.3, and 98 micrograms/ml, respectively. For SAA and its metabolites, the binding to plasma and milk proteins was determined. No glucuronide or sulphate conjugates of SAA and its acetyl metabolites could be found in plasma, milk, or urine. Based on the sensitivity of the bioassay (0.2 micrograms SAA/ml), a withholding time of 5 days was suggested for milk following single oral SAA dosage of 200 mg/kg.

Disposition of sulfadimidine and its N4-acetyl and hydroxy metabolites in horse plasma

The plasma disposition of sulfadimidine (SDM) and its metabolites N4-acetylsulfadimidine (N4-SDM), 6-hydroxymethyl-4-methyl-pyrimidine (SCH2OH) and 5-hydroxy-4,6-dimethyl-pyrimidine (SOH), was studied in three horses following intravenous administration of SDM at dose levels of 20 and 200 mg/kg in cross-over trials. The percentages of N4-SDM (0.58-0.90%), SOH (0.83-6.75%) and SCH2OH (0.38-0.71%) in plasma, expressed as a percentage of the total sulfonamide concentration, were small and their plasma concentrations were parallel with SDM from 4 h following administration. At high doses (200 mg/kg), the elimination half-life was slightly longer than at low doses (6.0, 10.5, 11.0 vs 5.0, 9.5, 9.5, respectively). The plasma protein binding was related to the dose; it was for the 20 and 200 mg/kg doses, respectively:SDM:61.5-73.3% and 50.5-52.1%; SOH: 47.1-71.0% and 36.7-39.5%, and for N4-SDM: 45.9-63.2% and 38.3-53.7%. The protein binding for SCH2OH, measured in samples obtained at the high dose level, ranged from 13.8 to 20.0%.

In vitro antimicrobial activity of hydroxy and N4-acetyl sulphonamide metabolites

Hydroxylated metabolites of sulphadimidine, sulphamerazine, sulphatroxazole, sulphamethoxazole, and sulphadiazine exhibited antimicrobial activity against Escherichia coli 28 PR 271 test strain ranging from 2.5 to 39.5 per cent of that of the parent drug. Trimethoprim addition potentiated the antimicrobial activity of these metabolites. N4-acetyl sulphonamide metabolites possessed no antimicrobial activity, nor did trimethoprim potentiated them.

Metabolism of the carbamate herbicide, asulam, in the rat

The metabolism of [ring-14C]asulam, a systemic herbicide highly effective against bracken, has been studied in rats. Most of the radioactivity (76-100% dose) administered orally or intravenously is excreted in the urine in 24 h as unchanged asulam (61-74% dose), N4-acetylasulam (8-14%) and N4-acetylsulphanilamide (0.1-2.6%). Small amounts of radioactivity (0.3-7.4% dose) were present in the faeces, only traces (0.2-0.3%) were excreted in the bile, and no significant 14CO2 was detected. Perfusion of rat liver with 14C-asulam resulted in more extensive metabolism. Total amounts present in perfusate (81% total), bile (1%) plus liver (14%) were 23.1% for unchanged asulam, 25.7% for acetylasulam, less than 1% for acetylsulphanilamide, and 4.5% as conjugates of asulam and acetylasulam, together with several other unidentified metabolites. Asulam is acetylated more readily than sulphanilamide, by rat-liver homogenate, and the highest enzyme activity was associated with the mitochondrial fraction (2.4 pmol/mg protein per min). Although not hydroxylated by rats in vivo, evidence was obtained for the hydroxylation of asulam by rat-liver microsomal preparations in vitro.