The antidotal potency of pyridinium oximes is as a result of reactivation of the phosphorylated cholinesterases.96,97 Oximes can reactivate phosphorylated cholinesterases via replacing the phosphoryl moiety from the enzyme. Phosphorylated oximes are produced learn more during this reaction and some of them seem to be potent inhibitors of AChE.98 The choice of oximes is based on the data presently available and may also be dependent on factors other than Inhibitors,research,lifescience,medical protection against lethality, such as cost and availability of the oximes and their side effects. Obidoxime (Toxogonin) is likely to cause more toxic effects than

pralidoxime and HI6. asoxime is the least toxic, but is less unstable in solution and is not commercially available in many parts of the

world.18 In soman-intoxicated guinea pigs, HI6 was therapeutically slightly more effective than HLo7, but was less effective than HLo7 against tabun intoxication.99 Pyridinium oximes are mostly used against OP-inhibited AChE in Inhibitors,research,lifescience,medical the peripheral nervous system and not as much in CNS. This is due to a limited penetration across the blood–brain Inhibitors,research,lifescience,medical barrier (BBB). However, it appears that the oximes penetrate BBB more than expected, since in soman poisoning oxime concentration in the brain was high.100 Recent studies in rats have shown that modulation of the BBB by a drug like tariquidar is of great value in enhancing the efficacy of oximes.101 The induction of local inflammatory processes and increase of brain–blood flow may also have some roles in enhancing the penetration of oximes through BBB. Sakurada et al have determined the amount of PAM-2 passing across the BBB at approximately 10% of the given dose. This amount may be effective in the reactivation of OP-inhibited AChE in

the brain. Inhibitors,research,lifescience,medical Inhibitors,research,lifescience,medical A new class of amidine-oxime reactivators of organophosphate (OP)-inhibited cholinesterases (ChE) have been reported to have increased BBB penetration with greater reactivation rates for OP-BuChE than pralidoxime (2-PAM) and monoisonitrosoacetone, but lower rates for OP-AChE reactivation compared to 2-PAM.102 In another study, the authors demonstrated that purified human and rabbit serum paraoxonase1 significantly protected against sarin and soman exposure in guinea pigs.103 Newly developed oximes (K206, K269) are relatively effective in reducing Adenosine cyclosarin-induced lethal toxic effects in mice. Their therapeutic efficacies exceed the therapeutic potency of obidoxime but not HI-6.104 Relative therapeutic effects of oximes in different OPs are presented in table 3. Table 3: Relative therapeutic effects of different oximes in organophosphate nerve agents poisoning Pralidoxime should be administered intravenously at 30 mg/kg initially over 30 min, followed by constant infusion of 8 mg/kg/hr in dextrose 5% solution.105 It could be continued until the full recovery or until atropine is required.