CORRECTION OF POSTTRANSPLANT ERYTHROCYTOSIS WITH ENALAPRIL

Erythrocytosis (i.e., elevation in red cell mass) frequently develops after renal transplantation and is associated with increased risk of t hromboembolic incidents and hypertension. Because it has been reported that enalapril may induce anemia in renal allograft recipients, we ha ve undertaken a prospective study to estimate the efficacy and safety of enalapril therapy for erythrocytosis and to establish the mechanism by which enalapril reduces red cell mass. Seventeen (12 male and 5 fe male) long-term renal allograft recipients with increased hematocrit v alue (> 55% for male and > 50% for female) and elevated red cell mass as determined with Cr-51-labeled autologous erythrocytes were treated with enalapril. After 3 months of therapy, enalapril was withdrawn and patients were observed in order to differentiate spontaneous remissio n of erythrocytosis from effects of enalapril therapy. After 3 months of the treatment, mean hematocrit decreased from 51.1% (range 47-56%) to 42.9% (range 37-51%; P<0.01). Red cell mass significantly decreased during this period (from 46.7 ml/kg, range 32.5-60.7 ml/kg, to 32.9 m l/kg, range 20.1-60.1 ml/kg; P<0.01). Serum erythropoietin levels also changed from 12.2 mIU/ml (range 1.0-33.0 mIU/ml) at baseline to 5.4 m IU/ml (range 0.7-24.2 mIU/ml; P<0.05). During the following 3 months w ithout enalapril treatment, an increase in hematocrit was noted, reach ing 51.7% (range 46-58%; P<0.05). No serious side effects of enalapril were observed during the study, but there was a need to reduce other hypotensive drugs in some patients. Serum creatinine did not change si gnificantly during enalapril therapy (1.49 mg/dl, range 0.9-2.3 mg/dl, and 1.55 mg/dl, range 1.0-2.3 mg/dl; before and after 3 months of the rapy, respectively). Our study proves that enalapril can be safely and effectively used to treat posttransplant erythrocytosis. The effect o f enalapril on red cell mass results from reducing erythropoietin prod uction.