The effect on heart rate of neuromuscular blockade reversal by pyridostigmine

Pyridostigmine without atropine, pyridostigmine with atropine or neostigmine with atropine were used to antagonise neuro-muscular blockade induced by d-tubocurarine in forty otherwise healthy, female patients recovering from gynaecological surgery. Pulse rates fell significantly (P less than 0.01, control heart rate 72 +/- 18 beats/min (M +/- SD) to 55 +/- 13 beats/min) at ten minutes after pyridostigmine (10 mg/70 kg), necessitating administration of atropine (1.25 mg/70 kg) by fifteen minutes after pyridostigmine. After an initial rise in rate, pulse rates also fell significantly (P less than 0.01, control heart rate 70 +/- 12 beats/min to 44 +/- 11 beats/min) at fifteen minutes after injection of neostigmine (2.5 mg/70 kg) with atropine (1.25 mg/70 kg). By contrast when pyridostigmine and atropine were used together, pulse rates rose and then fell, but mean values never fell below control during a twenty-minute observation period. It was concluded that pyridostigmine should not be given alone, but requires the use of atropine to prevent bradycardia. This combination may, however, provide a more stable heart rate than that seen with neostigmine and atropine in usual doses, when these drugs are used to antagonise d-tubocurarine.