Alcuronium requirement in patients receiving phenytoin--a case report

The effect of cerebral palsy on the action of vecuronium with or without anticonvulsants

Patients with cerebral palsy who are treated with anticonvulsant medication are resistant to vecuronium. We examined the contributions to vecuronium resistance made by cerebral palsy and anticonvulsants in a study of children with cerebral palsy and a control group. The acceleromyographic responses of the following three groups of children were studied: children with cerebral palsy not taking anticonvulsant medication (n = 11); children with cerebral palsy taking anticonvulsant medication (n = 8); and a control group of children who did not have cerebral palsy and were not taking anticonvulsant treatment (n = 10). Using a standardised technique, general anaesthesia was induced and maintained with 0.5-1. 5% isoflurane in a 60/40 nitrous oxide in oxygen mixture. After a stabilisation period which was performed with supramaximal train-of-four stimuli (2 Hz every 15 s) an intubating dose of vecuronium 0.1 mgkg-1 was administered. The first twitch of the train-of-four response (T1), the onset time, the times to 25, 50, 75 and 90% recovery of T1, recovery index, and the time to 70% recovery of train-of-four ratio were recorded. Recovery times to T1 and train-of-four responses were reduced significantly in both groups of children with cerebral palsy compared with the control group. These results suggest that children with cerebral palsy display resistance to vecuronium whether or not they are taking anticonvulsant drugs.

Phenytoin-induced resistance to vecuronium

Chronic phenytoin therapy causes resistance to some nondepolarising muscle relaxants. We have confirmed that this resistance is seen with vecuronium and suggest that at least a week of phenytoin therapy is required for a significant effect to develop. The mechanism of this resistance is not known. We have shown that an exaggerated rise in serum potassium after succinylcholine does not occur in patients with demonstrated resistance to vecuronium from chronic phenytoin therapy. This would suggest that significant extrajunctional acetylcholine receptor proliferation is an unlikely mechanism.