Pharmacokinetics in rabbits and anti-sphingomyelinase D neutralizing power of Fab, F(ab')2, IgG and IgG(T) fragments from hyper immune equine plasma

Abstract We describe the separation of whole IgG, IgG(T)-less IgG (called here merely IgG) and IgG(T) and the production of Fab and F(ab') 2 fragments. We studied the pharmacokinetics of these immunoglobulins and fragments in rabbits. Both, the isotypes and the whole IgG fragments were purified and/or produced from the same plasma lot from horses hyper immunized against sphingomyelinase D to produce anti- Loxosceles antivenom. The sphingomyelinase D neutralizing ability of the isotypes and their fragments was measured. Fab and F(ab') 2 PK was well described by a tri-exponential kinetics. IgG and IgG(T) PK, however, deviated from the tri-exponential kinetics 120 h after injecting a bolus of the immunotherapeutics. The departure between tri-exponential PK and the experimental data, was shown to be due to a surge of anti-horse antibodies occurring after 120 h, peaking at ≈ 260 h and decaying slowly afterward.