The duration of action of mivacurium is prolonged if preceded by atracurium or vecuronium

Isobolographic analysis of non-depolarising muscle relaxant interactions at their receptor site

Administration of certain combinations of non-depolarising muscle relaxants produces greater than expected neuromuscular blockade. Synergistic effects may be explained by drug interactions with the postsynaptic muscle nicotinic acetylcholine receptor. To investigate this hypothesis, the adult mouse muscle nicotinic acetylcholine receptor (alpha(2)beta delta epsilon) was heterologously expressed in Xenopus laevis oocytes and activated by the application of acetylcholine (10 microM). The effects of five individually applied muscle relaxants and six combinations of structurally similar and dissimilar compounds were studied. Drug combinations containing equipotent concentrations of two agents were tested and dose-response curves were determined. All compounds tested alone and in combination produced rapid and readily reversible, concentration-dependent inhibition. Isobolographic and fractional analyses indicated additive interactions for all six tested combinations. These findings suggest that synergistic neuromuscular blocking effects, observed for the administration of certain combinations of muscle relaxants, do not result from purely postsynaptic binding events at the muscle nicotinic acetylcholine receptor, but rather from differential actions on pre- and postsynaptic sites.

Increased sensitivity to rocuronium and atracurium in mitochondrial myopathy

PURPOSE

To describe the prolonged effect of the intermediate-acting, non-depolarising neuromuscular blocking agents rocuronium and atracurium in a 29-yr-old apparently healthy woman.

CLINICAL FEATURES

Because of abdominal pain the patient was scheduled for explorative laparoscopic pelvic examination. General anaesthesia was induced with fentanyl, midazolam and propofol. Muscle relaxation was achieved with 0.6 mg.kg-1 rocuronium. Anaesthesia was maintained with nitrous oxide and propofol. Two Hz train-of-four stimulation every 15 sec evoked no twitch responses until 60 min after rocuronium. Further relaxation was achieved with 0.075 mg.kg-1 atracurium after which twitch responses recurred after 45 min. Fifteen minutes later neuromuscular blockade was successfully reversed with atropine and neostigmine. The postanaesthetic course was uneventful. Because of the increased sensitivity to rocuronium and atracurium the patient was re-evaluated postoperatively. History revealed occasional double vision, fatigue, muscle cramps, stiffness and myoglobinuria. Clinical neurological examination showed ptosis, tremor, ataxia and bradydiadochokinesia. A standardised lactate stress testing on a bicycle was pathological and, after muscle biopsy, the diagnosis of mitochondrial myopathy was established.

CONCLUSION

An increased sensitivity to rocuronium and atracurium may occur in patients with mitochondrial myopathy. In these patients appropriate dosing of muscle relaxants and adequate monitoring of the neuromuscular blockade are required. If an increased sensitivity to rocuronium and atracurium occurs in an apparently healthy subject, further neurological investigations should follow.

The pharmacodynamics of mivacurium preceded by atracurium or cisatracurium in children

We evaluated whether mivacurium maintains its short duration of effect when preceded by atracurium or cisatracurium in 45 children during propofol/alfentanil/N2O/O2 anesthesia. Neuromuscular response was recorded by using an adductor pollicis electromyogram (EMG). Children were randomized to receive two doses of atracurium (350 micrograms/kg and 70 micrograms/kg in Group AM), cisatracurium (64 micrograms/kg and 10 micrograms/kg in Group CM), or mivacurium (200 micrograms/kg and 100 micrograms/kg in Group MM), followed by a final dose of mivacurium 100 micrograms/kg. The second and third doses of the muscle relaxants were administered at 25% EMG recovery. After the final dose of mivacurium, the times to 95% of EMG recovery in groups AM, CM, and MM were (median with 10-90 percentile range) 33.0 (28.0-40.0) min, 30.7 (26.0-40.3) min, and 10.3 (8.0-14.0) min, respectively (P < 0.0001). The recovery times to a train-of-four ratio of 0.70 were 30.3 (24.7-37.0) min, 28.0 (24.7-37.7) min, and 10.3 (8.0-13.7) min for groups AM, CM, and MM, respectively (P < 0.0001). Thus, the duration of effect of mivacurium was prolonged by 200% if preceded by either atracurium or cisatracurium.

IMPLICATIONS

We compared the pharmacodynamics of mivacurium given alone or preceded by atracurium or cisatracurium in children. The duration of effects of mivacurium was prolonged by 200% if preceded by either atracurium or cisatracurium. This implies that mivacurium has a short duration of effect only when given as a single relaxant.