title: Diurnal variation in the metabolism of S-carboxymethyl-L-cysteine in humans.
abstract: The routes of metabolism of S-carboxymethyl-L-cysteine in humans are dependent on the time of dosing. Administration of 750 mg of S-carboxymethyl-L-cysteine (Day 1) during the day at 8:00 AM followed by a 8:00 AM to 4:00 PM urine collection revealed that S-carboxymethyl-L-cysteine S-oxide was the major urinary metabolite produced. The 4:00 PM to midnight urine collection resulted in S-(carboxymethylthio)-L-cysteine being identified as the major urinary metabolite. However, the administration of 750 mg of S-carboxymethyl-L-cysteine (day 15) during the night at midnight and analysis of the midnight to 8:00 AM urine collection found that thiodiglycolic acid was the major urinary metabolite, whereas thiodiglycolic S-oxide was identified as the major urinary metabolite in the 8:00 AM to 4:00 PM urine collection. A diurnal variation in the metabolism of S-carboxymethyl-L-cysteine was seen and, in particular, the timing of S-carboxymethyl-L-cysteine administration had a profound effect on the identity of urinary S-oxide metabolites produced. After administration at 8:00 AM the urinary S-oxides produced were S-carboxymethyl-L-cysteine S-oxide and S-methyl-L-cysteine S-oxide but at midnight the major urinary S-oxide metabolite produced was thiodiglycolic acid S-oxide.
authors.affiliation: Department of Pharmacy, King's College London, London, United Kingdom. glyn.steventon@kcl.ac.uk
authors.forename: G B
authors.initials: GB
authors.lastname: Steventon
mesh_terms: D000328:Adult; D000891:Anti-Infective Agents, Local / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000652:urine; D001711:Biotransformation; D002233:Carbocysteine / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000652:urine; D002851:Chromatography, High Pressure Liquid; D002940:Circadian Rhythm / Q000502:physiology*; D006801:Humans; D008297:Male; D010084:Oxidation-Reduction
chemical_list: D000891:Anti-Infective Agents, Local; D002233:Carbocysteine