Recombinant erythropoietin has become a routine component of care of patients with chronic kidney disease reducing the need for blood transfusions but raising the risks for cardiovascular events. We undertook this secondary analysis of subjects enrolled in the Correction of Hemoglobin and Outcomes in Renal Insufficiency (CHOIR) trial to examine the interrelationships between epoetin-alfa maintenance doses utilized and achieved hemoglobin (Hb) irrespective of treatment target and randomized allocation.

We performed a post hoc analysis from the CHOIR trial. Inclusion criteria were Hb <11.0 g/dl and estimated glomerular filtration rates of 15-50 ml/min/1.73 m(2). To be included in the present analysis, subjects needed to be free of the composite event at 4 months, receive epoetin-alfa, and have ≥1 postbaseline Hb measurement. The mean weekly dose of epoetin-alfa received up to the time of first event or censure was the main exposure variable, while the achieved Hb at month 4 was the confounder representing the subject's underlying response to treatment. The primary outcome was the composite of death, heart failure hospitalization, stroke, or myocardial infarction. A Cox proportional hazard regression model was used in time-to-event analysis.

Among 1,244 subjects with complete data, the average weekly dose of epoetin-alfa ranged 143.3-fold from 133 to 19,106 units/week at the time of first event or censure. Cox proportional hazard analysis found that those in the middle tertile of Hb achieved (>11.5 to <12.7 g/dl) and the lowest tertile of epoetin-alfa dose exposure level (<5,164 units/week) had the lowest risk. Irrespective of Hb achieved, the relative risk in the highest tertile (>10,095 units/week) of epoetin-alfa dose exposure level was significantly escalated (hazard ratios ranged from 2.536 to 3.572, p < 0.05, when compared to the group of middle Hb tertile and lowered dose tertile). In a multivariable model that adjusted for achieved Hb, albumin, cholesterol, age, prior heart failure, prior stroke, prior deep venous thrombosis, atrial fibrillation or malignancy, the average weekly dose had a significant (p = 0.005) relative risk of 1.067 per 1,000 units of epoetin-alfa for the primary end point.

In the CHOIR trial, average epoetin-alfa doses >10,095 units/week were associated with increased risks for cardiovascular events irrespective of the Hb achieved within the first 4 months of treatment. These data suggest the weekly epoetin-alfa dose and not the Hb achieved was a principal determinant in the primary outcome observed implicating a cardiovascular toxicity of this erythrocyte-stimulating agent.