Clinical experience with
oximes,
cholinesterase reactivators used in
organophosphorus poisoning, has been disappointing. Their major anatomic site of therapeutic action and their ability to pass the blood-brain barrier (BBB) are controversial. Although their physico-chemical properties do not favour BBB penetration, access of
oximes to the brain may be facilitated by
organophosphates. The effect of the
organophosphate paraoxon (POX) on
pralidoxime (2-PAM) brain entry was therefore determined. Rats either received 50 micromol
2-PAM only (G(1)) or additionally 1 micromol POX ( approximately LD(75)) (G(2)). Three animals each were killed after 5, 15, 30, 60, 90, 120, 180, 240, 360, 480 min, and
2-PAM concentrations in the brain and plasma were measured using HPLC. Moreover, the effect of brain perfusion with isotonic saline on subsequent
2-PAM measurements was assessed. The maximal
2-PAM concentration (C(max)) in G(1) brain was 6% of plasma C(max), while in G(2) brains it was 8%. Similarly, the ratio of the area under the curve (AUC) brain to plasma was 8% in G(1) and 12% in G(2). Brain t(max) (15 min) was slightly higher than plasma t(max) (5 min). The AUC of plasma
2-PAM did not differ between G(1) and G(2). However, in G(1), AUC brain was significantly lower than in G(2), the differences probably being clinically irrelevant. In perfused brains,
2-PAM concentrations were very close to those of non-perfused brains. The results indicate that brain penetration of
2-PAM is poor and that
organophosphates only have a modest effect on
2-PAM BBB penetration. Brain perfusion does not significantly alter
2-PAM measurements and is therefore considered unnecessary.