Abstract
The routes of metabolism ofS-carboxymethyl-l-cysteine in humans are dependent on the time of dosing. Administration of 750 mg ofS-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 thatS-carboxymethyl-l-cysteineS-oxide was the major urinary metabolite produced. The 4:00 PM to midnight urine collection resulted inS-(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 ofS-carboxymethyl-l-cysteine was seen and, in particular, the timing ofS-carboxymethyl-l-cysteine administration had a profound effect on the identity of urinary S-oxide metabolites produced. After administration at 8:00 AM the urinaryS-oxides produced wereS-carboxymethyl-l-cysteineS-oxide andS-methyl-l-cysteine S-oxide but at midnight the major urinary S-oxide metabolite produced was thiodiglycolic acid S-oxide.
Footnotes
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Send reprint requests to: Glyn B. Steventon, Department of Pharmacy, King’s College London, Manresa Road, London SW3 6LX, United Kingdom. E-mail: glyn.steventon{at}kcl.ac.uk
- Abbreviations used are::
- SCMC
- S-carboxymethyl-l-cysteine
- SCMCSO
- S-carboxymethyl-l-cysteineS-oxide
- SMC
- S-methyl-l-cysteine
- SMCSO
- S-methyl-l-cysteineS-oxide
- TDA
- thiodiglycolic acid
- TDASO
- thiodiglycolic acid S-oxide
- CMTC
- S-(carboxymethylthio)-l-cysteine
- Received March 15, 1999.
- Accepted June 21, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
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