The effect of folate supplements on 6-mercaptopurine remission maintenance therapy in childhood leukaemia.

The effect of folic acid supplements on 6-mercaptopurine remission maintenance therapy in lymphoblastic leukaemia (ALL) was investigated in a retrospective longitudinal study of 10 children. Red cell concentrations of 6-thioguanine nucleotide, a cytotoxic metabolite of 6-mercaptopurine, were measured and the peripheral neutrophil count was used as an index of myelosuppression. During the control period of the study there were significant correlations between 6-mercaptopurine dose and 6-thioguanine nucleotide concentration (rs = 0.59, P less than 0.0005) and between 6-thioguanine nucleotide concentration and the peripheral neutrophil count at 14 days (rs = 0.58, P less than 0.0005). These relationships were absent when the same children were subsequently taking folate supplements. Also when taking folate supplements the children tolerated significantly more 6-mercaptopurine (P less than 0.005) for a significantly longer time (P less than 0.005) before neutropenia developed. There was no significant difference in red cell 6-thioguanine nucleotide concentration in the absence and presence of folate supplements. These findings suggest that folate supplements may interfere with remission maintenance therapy in ALL.