Convulsive thresholds in mice during the recovery phase from anaesthesia induced by propofol, thiopentone, methohexitone and etomidate.

1. Convulsive thresholds were measured with intravenous pentylenetetrazol in mice during the recovery phase after intravenous anaesthetic doses of propofol (10 and 20 mg kg-1), thiopentone (30 mg kg-1), methohexitone (10 mg kg-1), and etomidate 3 mg kg-1). 2. The convulsive threshold rose after each agent, indicating an anticonvulsant action for all the drugs tested; this declined to control values with initial half times of: 1.56 min (propofol 10 mg kg-1); 1.03 min (propofol 20 mg kg-1): 1.02 min (methohexitone); 3.35 min (etomidate); 13.7 min (thiopentone). 3. At no time during the recovery phase of any agent did the convulsive threshold fall below control values, which might indicate an epileptogenic effect of the drug. 4. The threshold was depressed below control values by intravenous administration of Ro 15-4513, a partial inverse agonist at the benzodiazepine receptor, thus indicating the ability of this pentylenetetrazol test to demonstrate a proconvulsant effect. 5. We conclude that the abnormal movements or convulsions associated with recovery from anaesthesia with short-acting intravenous anaesthetics may not be the result of an intrinsic proconvulsant action of the drugs.