Interpatient variability in duration of action occurs with mivacurium as with other neuromuscular-blocking agents. Has no known effect on consciousness, pain threshold, or cerebration (to avoid distress to the patient, neuromuscular block should not be induced before unconsciousness). The duration of action may be prolonged in patients with reduced plasma cholinesterase (pseudocholinesterase) activity (lower infusion rates are recommended in these patients; caution in patients known to be or suspected of being homozygous for the atypical plasma cholinesterase gene). Severe anaphylactic reactions to neuromuscular-blocking agents, including mivacurium, have been reported (precautions should also be taken in those individuals who have had previous anaphylactic reactions to other neuromuscular-blocking agents). Injection is acidic (pH 3.5 to 5.0) and may not be compatible with alkaline solutions having a pH greater than 8.5 (e.g. barbiturate solutions). Multiple-dose vials of mivacurium contain benzyl alcohol (exposure to excessive amounts of benzyl alcohol has been associated with toxicity (hypotension, metabolic acidosis), particularly in neonates). Although mivacurium chloride is not a potent histamine releaser, the possibility of substantial histamine release must be considered (caution in patients with cardiovascular disease and patients with any history suggesting a greater sensitivity to the release of histamine or related mediators (e.g. asthma)). Neuromuscular-blocking agents may have a profound effect in patients with neuromuscular diseases (e.g. myasthenia gravis and the myasthenic syndrome) and other conditions in which prolonged neuromuscular block is a possibility (e.g. carcinomatosis), the use of a peripheral nerve stimulator and a dose adjustment is recommended to assess the level of neuromuscular block and to monitor dosage requirements. Antagonists (such as neostigmine) should not be administered when complete neuromuscular block is evident or suspected.