Some of the views expressed in the following notes on newly approved products should be regarded as preliminary, as there may have been limited published data at the time of publication, and little experience in Australia of their safety or efficacy. However, the Editorial Executive Committee believes that comments made in good faith at an early stage may still be of value. Before new drugs are prescribed, the Committee believes it is important that more detailed information is obtained from the manufacturer's approved product information, a drug information centre or some other appropriate source.
Mivacron (Glaxo Wellcome)
2 mg/mL in 5 mL, 10 mL and 25 mL ampoules
Indication: muscle relaxation
Intubation in general anaesthesia requires muscle relaxation. This can be achieved by antagonising the action of acetylcholine to block neuromuscular transmission. Mivacurium is a non -depolarising neuromuscular blocker which binds competitively to cholinergic receptors on the motor end-plate. It is a mixture of 3 stereoisomers and has a structure similar to atracurium.
Within a few minutes of intravenous injection, maximum blockade is achieved. However, mivacurium has a shorter duration of action than other non-depolarising neuromuscular blocking drugs. This means that the patient quickly recovers and may not require a reversal drug e.g. neostigmine.
To maintain neuromuscular block, mivacurium can be given by continuous infusion. The rate of infusion is adjusted at intervals of at least 3 minutes according to the clinical response. The half-life is less than two minutes with the termination of the blockade depending on hydrolysis by pseudo cholinesterase.
Mivacurium activity is influenced by some disease states, e.g. hepatic dysfunction, and other drugs. The neuromuscular block can be potentiated by inhaled anaesthetics such as halothane. It is also increased by diuretics, propranolol, lignocaine, calcium channel blockers and some antibiotics.
Like atracurium, mivacurium can provoke the release of histamine from mast cells. Although hypotension and bronchospasm can be precipitated, flushing is more commonly observed, occurring in 15% of patients.
