Phencyclidine-specific Fab fragments alter phencyclidine disposition in dogs

High affinity antibodies (K₀ = 3 x 10⁹ M^-1) against the widely abused drug phencyclidine (PCP) were produced in goats and then purified and extensively characterized for use in in vivo pharmacokinetic studies. An iv dose of ³H-PCP was administered to three dogs, followed 2 hr later by an equimolar dose of PCP-specific antigen-binding fragments (Fab). Within 10 min after Fab administration, the concentration of PCP in the serum had increased 17-56-fold in the three dogs. The Fab administration also produced a 10-fold decrease in volume of distribution and in systemic and renal clearances. The concentration of PCP metabolites decreased for a period of time after Fab administration. Equilibrium dialysis studies showed that the percentage of unbound PCP changed from about 50% before Fab administration to <1% unbound after Fab. In addition, the blood/plasma ratio of PCP changed from a near-equal distribution between red blood cells and plasma before Fab to virtually all of the drug being confined to the plasma fraction after Fab administration. Although Fab produced a dramatic redistribution and extensive protein binding of PCP, the route of elimination of PCP was not altered. These data suggest that high affinity anti-PCP Fab could reverse the toxicity of PCP.