Biotransformation of 6-thioguanine in inflammatory bowel disease patients: a comparison of oral and intravenous administration of 6-thioguanine |
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Authors: | Jharap B de Boer Nkh Vos Rm Smid K Zwiers A Peters Gj Mulder Cjj Wilhelm Aj van Bodegraven Aa |
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Affiliation: | 1Gastroenterology and Hepatology, VU University Medical Center, Amsterdam, the Netherlands;2Clinical Pharmacology and Pharmacy, VU University Medical Center, Amsterdam, the Netherlands;3Medical Oncology, VU University Medical Center, Amsterdam, the Netherlands;4Molecular Celbiology and Immunology, VU University Medical Center, Amsterdam, the Netherlands |
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Abstract: | BACKGROUND AND PURPOSEAlthough 6-mercaptopurine and azathioprine are effective treatments in inflammatory bowel disease (IBD), many patients discontinue treatment because of side effects. 6-Thioguanine (6-TG) may be an alternative rescue therapy in these intolerant patients but the pharmacokinetics of 6-TG are not fully described. Here we have measured the pharmacokinetics of the biotransformation of 6-TG into the pharmacologically active metabolites, 6-thioguanine nucleotides (6-TGN), in IBD patients.EXPERIMENTAL APPROACHIn 12 patients with IBD, levels of 6-TGN and activities of thiopurine S-methyltransferase, xanthine oxidase and hypoxanthine guanine-phosphoribosyl-transferase were measured in a two-stage (i.v. and p.o. administration of 0.3 mg·kg−1 6-TG), prospective study. Median exposure of 6-TGN in red blood cells (RBC) was expressed as the ratio of the area under the curve (AUC) per mg 6-TG after i.v. dosing and that after p.o. dosing.KEY RESULTSThe median AUC per mg 6-TG was 1068 (p.o.) and 7184 (i.v.) pmol·h (8 × 108 RBC)−1. Median exposure of 6-TGN in RBC was 15% (9–28). Hypoxanthine guanine-phosphoribosyl-transferase activity correlated with peak 6-TGN and with AUC per mg (r = 0.7, P = 0.02 and r = 0.6, P = 0.03 respectively). Thiopurine S-methyltransferase activity was inversely related to AUC per mg (r=−0.8, P = 0.001), whereas that of xanthine oxidase was correlated with a lower peak 6-TGN (r=−0.7, P = 0.02).CONCLUSIONS AND IMPLICATIONSThe great variability of the AUC per mg for 6-TG observed after p.o. and i.v. administration of 6-TG, was partly explained by variability in activities of metabolizing enzymes. Exposure of 6-TGN was low in all patients. |
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Keywords: | pharmacokinetics 6-thioguanine 6-thioguanine nucleotides inflammatory bowel disease TPMT XO HGPRT |
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