Summary
In response to reports of discrepant in vitro assays of high-purity concentrates,
a double-blind crossover study of in vivo recovery and half-life of two brands of
monoclonal-antibody-purified factor VIII concentrates (Monoclate and Hemofil-M) was
performed in 23 patients with hemophilia A. In vivo recoveries were close to values
predicted from the labelled unitage when plasma samples were assayed by a one-stage
method. When a two-stage assay was used, lower recoveries were calculated and the
recovery with Hemofil-M was slightly but significantly lower than that with Monoclate.
The concentrates were re-assayed in vitro by the two-stage method. Monoclate (which
is assayed by the manufacturer using a two-stage method) contained 97% of the labelled
potency and Hemofil-M (which is assayed by the manufacturer using a one-stage method)
contained 81% of the labelled potency. Differences in in vitro and in vivo assay methods
contribute to disparities between expected and observed factor VIII recovery. Clearance
of Hemofil-M was significantly faster than that of Monoclate, but volume of distribution
at the steady state, mean residence time, and plasma half-disappearance times of the
two concentrates were not significantly different.
