Impaired Reticuloendothelial Function in Patients Treated with Methyldopa

In about 20 per cent of patients taking the antihypertensive agent methyldopa, IgG autoantibodies form against red cells, but most such patients do not have hemolysis. The reason for this is uncertain; it does not appear to be explained by known characteristics of the autoantibody. Since antibody-dependent reticuloendothelial function is an important determinant of cell clearance, we measured reticuloendothelial function in nine patients taking methyldopa. We did this by measuring the rate of clearance of radiolabeled autologous red cells sensitized with anti-D alloantibody. Five patients had a positive direct antiglobulin test, and four did not. Only one patient had laboratory evidence of hemolysis. The patients without hemolysis had significantly impaired reticuloendothelial clearance. In contrast, the patient with hemolysis did not have impaired reticuloendothelial function. This study suggests that in patients taking methyldopa who have a positive direct antiglobulin test the absence of hemolysis may be caused by an impairment in reticuloendothelial function. That the drug itself may be responsible for the impairment is suggested by the occurrence of abnormal reticuloendothelial function in patients taking the drug who have a negative direct antiglobulin test.