Convulsions induced by hyperbaric oxygen: inhibition by phenobarbital, diazepam and baclofen.

1. The anticonvulsive potencies of diazepam, phenobarbital and baclofen against convulsions induced by oxygen under high pressure (OHP), by isoniazid and by strychnine were investigated in mice and rats. 2. The anticonvulsive potency of diazepam was much higher than that of phenobarbital and baclofen against all three types of convulsions. 3. The selective activity of diazepam against isoniazid induced convulsions in rats (dose ratio ED50 phenobarbital/ED50 diazepam: 400) could not be confirmed in mice (dose ratio ED50 phenobarbital/ED50 diazepam: 20-40), where diazepam was equipotent against all three types of convulsions. 4. Baclofen which does not inhibit strychnine induced convulsions was equipotent in inhibiting convulsions evoked by isoniazid and OHP in mice. 5. The results are in agreement with the postulated GABA-inhibitory mechanism of OHP induced convulsions, whereas they make a glycine inhibitory mechanism very unlikely. Although the results do not allow further conclusions about the mode of action of diazepam, a clinical trial of diazepam in OHP-induced convulsions should be considered.