Effect of neostigmine and pyridostigmine on the plasma cholinesterase activity

The effect of neostigmine 0.05 mg kg-1 or pyridostigmine 0.25 mg kg-1 on serum cholinesterase activity was investigated in 20 adult patients undergoing elective surgery. Both drugs produced marked depression of enzymatic activity. The maximal depression was observed in samples taken 5 min after injection. The maximal percentage depression of enzymatic activity was not significantly different in the two drug groups. However, at 30-60 min after injection, the degree of depression was less in the neostigmine group. This may be attributed to the different plasma clearances of neostigmine and pyridostigmine.