Diazepam is a commonly used drug for suicidal attempts. The antagonistic effect of physostigmine in these patients is poorly understood.

We studied the interaction of large doses of diazepam and either physostigmine or galanthamine hydrobromide using dose-response curves in 21 cats. After establishing dose-response curves for diazepam, half of the animals received 0.02 mg/kg of physostigmine intravenously. Two minutes later 8, 10, 12, or 14 mg/kg of diazepam was administered intravenously. After 2, 5, and 10 min, animals were evaluated for their response to noise and pain stimuli. The other half of animals were given 0.2 mg/kg of galanthamine intravenously and evaluated for diazepam effect using the same criteria. Sufficient number of days were allowed for the animals to recover from diazepam.