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On the limitation of 6-tioguaninenucleotide monitoring during tioguanine treatment.

de Boer NK, de Graaf P, Wilhelm AJ, Mulder CJ, van Bodegraven AA

Gastroenterology and Hepatology, VU University Medical Centre, The Netherlands.

BACKGROUND: Tioguanine (thioguanine) has been proposed as a rescue thiopurine for azathioprine or mercaptopurine intolerant inflammatory bowel disease patients. The use of tioguanine leads to high 6-tioguaninenucleotide (6-thioguaninenucleotide) levels in red blood cells but, contra-intuitively, these have yet not been associated with an increased risk of myelotoxicity. AIM: To assess the role of 6-tioguaninenucleotide concentrations in developing myelotoxicity during tioguanine treatment. METHODS: Database analysis of 25 patients treated with tioguanine. Clinical findings and laboratory parameters were related to 6-tioguaninenucleotide levels. RESULTS: One patient developed a myelodepression (21 mg TG/day for 3 months and 6-tioguaninenucleotide 714 pmol/8 x 10(8) red blood cells). 6-Tioguaninenucleotide levels varied greatly between individuals (mean 6-tioguaninenucleotide level 621 pmol/8 x 10(8) red blood cells, s.d. 340 pmol/8 x 10(8) red blood cells and range 34-1653 pmol/8 x 10(8) red blood cells). The TG dosages (mean 20.6 mg/day and median 20 mg/day) did not correlate with 6-tioguaninenucleotide levels (r = 0.31, N.S.). High 6-tioguaninenucleotide levels (>450 pmol/8 x 10(8) red blood cells) did not effect haemoglobin concentrations (mean 8 mmol/L), peripheral leucocyte (mean 7.5 x 10(9)/L) or platelet counts (mean 298 x 10(9)/L). No correlations were established between laboratory parameters, type of disease and 6-tioguaninenucleotide level. CONCLUSION: High 6-tioguaninenucleotide levels in erythrocytes (>450 pmol/8 x 10(8)) during TG treatment compared to azathioprine or mercaptopurine treatment are not indicative for (developing) myelotoxicity.

Published 30 August 2005 in Aliment Pharmacol Ther, 22(5): 447-51.
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