Anaphylaxis caused by neostigmine

We read with interest the case report of ‘Anaphylaxis caused by neostigmine’ (Seed & Ewan. Anaesthesia 2000; 55: 574–5), and noted particularly that edrophonium was suggested as a safe alternative for future use. We feel that although edrophonium can be used to reverse neuromuscular blockade, it should not be regarded as a straightforward substitute for neostigmine. There are several reasons for this. Firstly, as has been widely described, edrophonium is very short acting. Matteo et al., investigating edrophonium in elderly patients, noted that the maximum duration of action is very brief (1.3–2.2 min), whereas the value for neostigmine is several times greater [1]. Second, the dose–response relationship is different. Naguib and Abdulatif demonstrated that the dose–response curves for reversal of neuromuscular blockade are not parallel for neostigmine and edrophonium [2]. Third, at usual therapeutic dosage, a greater proportion of patients treated with edrophonium will fail to achieve adequate reversal, where this is defined as a train-of-four ratio (TOF) of 0.7. The British National Formulary gives a dosage of 500–700 µg.kg−1 for edrophonium and 50–70 µg.kg−1 for neostigmine. Lavery et al. compared edrophonium and neostigmine at these dosages for reversal of atracurium-induced blockade. They achieved adequate reversal in all patients treated with neostigmine but in only 13 out of 20 patients treated with edrophonium [3]. Of note, given that an impaired ventilatory response to hypoxaemia can be demonstrated up to a TOF ratio of 0.9, a value of 0.7 may be regarded as a minimum standard [4]. In our experience, edrophonium is infrequently used for reversal of neuromuscular blockade. We would prefer to avoid its use. For the reasons described we believe that there is a greater risk of inadequate reversal or recurarisation than with neostigmine.