β-Eudesmol as an antidote for intoxication from organophosphorus anticholinesterase agents

β-Eudesmol, a sesquiterpenol present in Chinese herbs, improved the tetanic contraction impaired by diisopropylfluorophosphate in isolated mouse diaphragm preparations by an inhibition of the regenerative acetylcholine release. The antagonism was enhanced when a small concentration of obidoxime was present. Neither enzyme reactivation nor curare-like action was evident. β-Eudesmol (300 mg/kg, i.p.) elevated the LD₅₀ of diisopropylfluorophosphate (s.c.) in control mice from 4.2 to 6.4 mg/kg and in mice pretreated with atropine from 7.8 to 10.6 mg/kg. In mice pretreated with atropine and obidoxime, β-eudesmol showed a greater synergistic effect, increasing the LD₅₀ from 281 to more than 800 mg/kg. β-Eudesmol also markedly alleviated diisopropylfluorophosphate-induced muscle fasciculation, tremor and convulsion and prolonged the time to death. It is proposed that β-eudesmol may be added to the standard antidotal regimen (atropine plus obidoxime) for treating organophosphate intoxication.