RESUMO
Objective To evaluate the effect and mechanism of 5-aminosalicylic acid (5-ASA) on bone marrow suppression caused by thiopurines, and to explore the proper dosage of thiopurines when combined with 5-ASA for inflammatory bowel diseases (IBD) patients.MethodsThe clinical data of IBD patients who took thiopurines were retrospectively analyzed. Thiopurine methyltransferase (TPMT) activity and 6-thioguanine nucleotide (6-TGN) concentration were tested.In prospective study, patients firstly treated with azathioprine (AZA) of 50 mg/d for 4 weeks, then combined with 5-ASA of 3 g/d for another 4 weeks.The concentration of 6-TGN in red blood cells (RBC) was analyzed at the end of 4th and 8th week.Results In retrospective study, there were 45 cases in AZA/6-mercaptopurine (MP) combined with 5-ASA group, 94 patients were in AZA/6-MP.alone group.The incidence of bone marrow suppression in these two groups were 46.7％ and 16.0％, respectively.Multivariates regression analysis indicated co-administration of 5-ASA was the only risk factor of increasing bone marrow suppression incidence (OR=3.45,95％ CI 1.31 ～ 9.04).There was no significant difference of TPMT activity between AZA/6-MP combined with 5-ASA group and AZA/6-MP alone group(t=-0.351 ,P=0.734).The 6-TGN concentration was significantly higher in AZA/6-MP combined with 5-ASA group than that of AZA/6-MP alone group (the median concentration was 384.9 pmol/8× 108 RBC and 286.4 pmol/8× 108 RBC,F=29.15,P=0.00).Prospective study was completed in 8 patients.After treated with AZA of 50 mg/d for 4 weeks, the 6-TGN concentration of 7 patients was lower than 230 pmol/8 × 108 RBC.After added with 5-ASA of 3 g/d for another 4weeks, the 6-TGN concentration of 7 patients was over 230 pmol/8 × 108 RBC, three patients of those was even higher than 420 pmol/8 × 108 RBC, and bone marrow suppression occurred in 2 patients.ConclusionsThe incidence of bone marrow suppression increased in Chinese IBD patients treated with recommended routine dossage of AZA/6-MP when conbined with 5-ASA.The mechanism may be related with the increased concentration of 6-TGN in RBC.To reduce the AZA dosage may possibly keep the efficacy while decrease the incidence of bone marrow suppression.
