A randomized placebo-controlled study of enalapril in the treatment of erythrocytosis after renal transplantation

Background. Erythrocytosis is a common complication of renal transplantation with an incidence of up to 17%. It is associated with an increased risk of complications due to thromboembolic events and has traditionally been treated by intermittent venesection. More recently, angiotensin-converting enzyme inhibitors have been shown to cause a fall in haematocrit in a number of groups of subjects and some uncontrolled studies have shown these drugs to be of possible therapeutic benefit in post renal transplant erythrocytosis. Methods. We performed a randomized double-blind placebo-controlled study in 25 patients with post-transplant erythrocytosis. Subjects received either 2.5 mg of enalapril daily or a placebo for 4 months and all patients completed the study period without any serious adverse effects. Results. Haematocrit fell from 52.7 (±SEM 0.7) to 47.1 (±1.8) at 1 month and 46.1 (±1.2) after 4 months in patients receiving enalapril, with no change in the placebo group (P=0.004). We did not demonstrate any change in serum erythropoietin in either group. Conclusions. Angiotensin-converting enzyme inhibitors are a safe and effective form of treatment for erythrocytosis developing after renal transplantation. The mechanism of action, however, is not mediated by changes in erythropoietin production and remains uncertain.