Red cell abnormalities associated with sulphasalazine maintenance therapy for ulcerative colitis

Of 52 patients receiving a mean dose of 2.5g sulphasalazine/day as maintenance therapy for ulcerative colitis, 35 were found to have one or more drug-induced red cell abnormalities, which were not found in 50 normal controls or in 10 colitics not receiving sulphasalazine. Twenty-three of the treated patients had contracted red cells, an abnormality that is thought to result in mild haemolysis. Red cell contraction was related to the dose of sulphasalazine (P smaller than 0.01), the serum total sulphapyridine level (P smaller than 0.001), and acetylator status. Eleven of the treated patients had a macrocytosis, 21 had elevated levels of methaemoglobin, and one had Heinz bodies. A dose of 1.5 g sulphasalazine/day was not associated with red cell contraction, and is suggested as a safer maintenance dose for the asymptomatic colitic.