Impact of being underweight or overweight on factor VIII dosing in hemophilia A patients

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Abstract
Since 1981, the number of factor VIII units to infuse into patients with hemophilia A in order to achieve adequate circulating factor VIII levels has been calculated using the formula: [body weight(kg)× desired factor VIII increase(%)]/2, assuming a factor VIII recovery value of 2 for all patients. This study's aim was to evaluate the impact of several morphometric parameters and various coagulation factor concentrates on factor VIII recovery.The analysis included 201 hemophilia A adults (>18 years of age) who were carefully selected from eight pharmacokinetic clinical trials using three recombinant factor VIII concentrates (Advate®, Kogenate® FS, or ReFactoAF®/Xyntha®). Regression tree analysis was used to identify factor VIII recovery predictors. The median factor VIII recovery was 2.16 for all patients. Using regression tree analysis, patients were separated into three groups on the basis of body mass index: below 20.3 kg/m(2), between 20.3 and 29.5 kg/m(2), and 29.6 kg/m(2) or more. Each group had a significantly different median factor VIII recovery (P<0.001): 1.60, 2.14, and 2.70, respectively. The type of coagulation factor concentrate had no influence on recovery in the regression tree. In conclusion, factor VIII dosing should be adapted to underweight and overweight patients, as a factor VIII recovery of 2 does not apply to these patients. Ideal body weight should be considered instead of actual body weight in the dose calculations.

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