Plasma concentration of pyridostigmine during the antagonism of neuromuscular block.

The plasma concentrations of pyridostigmine were measured in eight patients during the antagonism of non-depolarizing neuromuscular blockade. After the injection i.v. of pyridostigmine bromide 14.6 mg/70 kg, the concentration of the drug rapidly decreased between 2 and 7 min, and then declined more slowly. After 2 h, significant amounts of pyridostigmine were still present in the plasma of all subjects. In the eight patients studied, the initial half-life was 1.0 +/- 0.3 min and the terminal half-life was 46.4 +/- 6.5 min (mean +/- SEM). Total body clearance of pyridostigmine was 8.7 +/- 1.5 ml min-1 kg-1, and the total apparent volume of distribution was 536 +/- 80 ml kg-1. Possible explanations for the differences between these results and previous studies are considered.