The effects of commonly used intravenous anaesthetic agents ketamine, thiopental sodium and propofol on the caffeine-alone or halothane-plus-caffeine-induced muscle contractures were investigated to determine safety for use in patients susceptible to malignant hyperthermia (MH). The muscle strips from rat diaphragm were exposed to one of these anaesthetic agents prior to challenge with caffeine 8 mmol/l alone or halothane 3% plus caffeine 8 mmol/l together. None of the three agents induced contractures when added alone. Ketamine 100 mumol/l and thiopental sodium 300 mumol/l augmented neither caffeine-alone nor caffeine-with-halothane contractures significantly and these two agents appear to be safe for use in MH-susceptible patients. In contrast, propofol 150 mumol/l augmented these contractile responses significantly and may not be recommended for use in patients known to be susceptible to this anaesthetic complication
