title: Influence of 5-aminosalicylic acid on 6-thioguanosine phosphate metabolite levels: a prospective study in patients under steady thiopurine therapy.
abstract: OBJECTIVE
  5-aminosalicylate (5-ASA) raises levels of 6-thioguanine nucleotides (6-TGN), the active metabolites of thiopurines such as azathioprine (AZA). Changes in levels of each individual TGN - 6-thioguanosine mono-, di- and triphosphate (6-TGMP, 6-TGDP, 6-TGTP) - and of 6-methylmercaptopurine ribonucleotides (6-MMPR) after 5-ASA are not known.
  
  
  METHODS
  Effects of increasing 5-ASA doses on AZA metabolites were investigated prospectively in 22 patients with inflammatory bowel disease in 4-week study periods. Patients started with 2 g 5-ASA daily, and then were increased to 4 g daily and followed by a washout period. Thiopurine doses remained unchanged throughout the entire study. Levels of 6-TGMP, 6-TGDP, 6-TGTP and 6-MMPR as well as of 5-ASA and N-acetyl-5-aminosalicylic acid (N-Ac-5-ASA) were determined each study period.
  
  
  RESULTS
  Median baseline levels in 17 patients of 6-TGDP, 6-TGTP and 6-MMPR were 52, 319 and 1676 pmol per 8 x 10(8) red blood cells respectively. After co-administration of 2 g 5-ASA daily, median 6-TGDP and 6-TGTP levels increased but median 6-MMPR levels were unchanged. Increasing 5-ASA to 4 g daily did not affect median 6-TGDP and 6-TGTP levels, but median 6-MMPR levels decreased. After discontinuation of 5-ASA, both 6-TGDP and 6-TGTP levels decreased and median 6-MMPR levels increased. The 6-TGTP/(6-TGDP+6-TGTP)-ratio did not change during the study, but 6-MMPR/6-TGN ratios decreased.
  
  
  CONCLUSIONS
  Individual 6-TGN metabolites increased after addition of 5-ASA, but 6-MMPR-levels and the 6-MMPR/6-TGN ratios decreased. Further studies are needed to decide whether this pharmacokinetic interaction would result in improvement of efficacy and/or increased risk of toxicity of AZA.
authors.affiliation: Clinical Pharmacology & Pharmacy, VU University Medical Center, Amsterdam, the Netherlands. Peer.deGraaf@vumc.nl
authors.forename: P
authors.initials: P
authors.lastname: de Graaf
authors.forename: N K H
authors.initials: NK
authors.lastname: de Boer
authors.forename: D R
authors.initials: DR
authors.lastname: Wong
authors.forename: S
authors.initials: S
authors.lastname: Karner
authors.forename: B
authors.initials: B
authors.lastname: Jharap
authors.forename: P M
authors.initials: PM
authors.lastname: Hooymans
authors.forename: A I
authors.initials: AI
authors.lastname: Veldkamp
authors.forename: C J J
authors.initials: CJ
authors.lastname: Mulder
authors.forename: A A
authors.initials: AA
authors.lastname: van Bodegraven
authors.forename: M
authors.initials: M
authors.lastname: Schwab
mesh_terms: D000328:Adult; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology*; D001379:Azathioprine / Q000493:pharmacokinetics* / Q000627:therapeutic use; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004359:Drug Therapy, Combination; D005260:Female; D006801:Humans; D007166:Immunosuppressive Agents / Q000493:pharmacokinetics*; D015212:Inflammatory Bowel Diseases / Q000188:drug therapy / Q000378:metabolism*; D008297:Male; D015122:Mercaptopurine / Q000493:pharmacokinetics / Q000627:therapeutic use; D019804:Mesalamine / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology*; D008875:Middle Aged; D011446:Prospective Studies
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; D007166:Immunosuppressive Agents; D019804:Mesalamine; D015122:Mercaptopurine; D001379:Azathioprine