Comparison of Factor VIII concentrates in non-bleeding patients.

:  The comparison of in vivo recovery of Factor VIII:C of 3 Factor VIII concentrates in two consecutive cross-over studies on non-bleeding patients suffering from a severe hemophilia A showed in both instances equally strong differences; values more than twice as high were obtained with product C than with product A. The cause for this was found to lie in the different declarations of the products. With calculations based on the results of the in vitro testing of the concentrates, the recoveries of the 3 products largely converged. For this reason one should demand that declarations for all products be made in accordance with uniform rules. In both studies the mean values of the half elimination times (half-lives) of Factor VIII:C were in each case the same for the 3 products; but in study a) the mean value of half-lives was distinctly longer (14.1 hrs) than in study b) (10.5 hrs). The recovery, too, was higher in study a) (1.96 YO) per injected unit measured than in study b) (1.4%). This occurred despite identical conditions in both studies. An explanation for this was not found. There was a tendency towards a positive relationship between recovery and body weight. According to the applied cross-over design, the rank order of the Factor VIII:C recoveries found between the various concentrates were not blurred by the individual differences from patient to patient; nor were they blurred by the strong varying hematocrit values and other unknown factors relating to deviations in recovery, distribution time and elimination time from patient to patient. There can be no doubt as to the advantages of the cross-over methodoly when performing direct in vivo comparisons.