The hydrolysis of suxamethonium in human blood

In 30 patients, after induction of anaesthesia, the ulnar nerve on both arms was stimulated, and the resulting had contractions recorded or closely observed. Immediately after the circulation to one arm had been occluded with a tourniquet, suxamethonium 1 mg/kg was injected i.v. The occlusion was relieved after 1, 2 or 3 min. It was found that the duration of block on the occluded arm represented 68, 48 and 19% of the non-occluded arm after 1, 2 and 3 min occlusion respectively. Thus a considerable recirculation of the drug occurs, even 3 min after injection. It can be calculated that the disappearance of suxamethonium from blood is 7.7 mg/litre in the 1st min and 2.9 mg/litre in both the 2nd and the 3rd min. These disappearance rates include both hydrolysis and diffusion from plasma. Thus the rate for hydrolysis contrasts sharply with the published values for suxamethonium hydrolysis in vitro.