EFFECT OF CIMETIDINE PRETREATMENT ON ROCU RONIUM-INDUCED NEUROMUSCULAR BLOCK

Cimetidine is a commonly used H-2-receptor antagonist that has been re commended for the prevention of acid aspiration syndrome and has been shown to potentiate vecuronium-induced neuromuscular block. The presen t study was designed to investigate the influence of a single IV dose of cimetidine on the neuromuscular effects of rocuronium, an analogue of vecuronium with a short onset time. Methods. Twenty adults aged 18- 65 years were included in the study with their informed consent and ap proval of the Ethics Committee. Following oxazepam premedication, 10 p atients were randomly allocated to receive cimetidine 400 mg IV 30 min before anaesthesia. After fentanyl and thiopentone induction, single- twitch stimulation of the ulnar nerve was performed every 10 s. Follow ing stabilisation of control responses, patients received rocuronium 0 .6 mg/kg for intubation. Anaesthesia was maintained with enflurane les s than or equal to 0.8 vol.% (end-tidal) and 65% nitrous oxide. Onset time and recovery times to 25% and 75% of the twitch control values we re recorded. Results. Onset and recovery times did not differ between groups. Conclusions. The results of the present study demonstrate that cimetidine does not increase the duration of rocuronium neuromuscular blockade. Inhibition of the cytochrome P450 system or a direct effect at the neuromuscular junction have been suggested as the mechanisms o f drug interaction associated with cimetidine. Impairment of hepatic m icrosomal drug metabolism results in a prolonged duration of action of vecuronium, which appears to be eliminated primarily via the liver. D ata on the elimination pathway of rocuronium in humans are not availab le. The fact that cimetidine does not alter the recovery from rocuroni um-induced neuromuscular block confirms a previous suggestion that roc uronium may not be eliminated principally by the liver. A direct effec t of cimetidine on the neuromuscular junction not be confirmed by this Therefore, cimetidine can be given as premedication without a risk of prolonged rocuronium block.