Neuromuscular function and plasma drug levels in pyridostigmine treatment of myasthenia gravis.

In 18 patients with generalised myasthenia treated with oral pyridostigmine, muscular strength, decrement of neuromuscular transmission in the trapezius muscle on repetitive accessory nerve stimulation, and pyridostigmine plasma level were measured repeatedly during 1-3 dosing intervals. Significant correlations between pyridostigmine concentrations and functional parameters were present in three out of 11 cases in which plasma levels changed by at least 25 ng/ml during the investigational period and peak levels did not exceed 100 ng/ml. Several other observations indicated that pyridostigmine at levels above 100 ng/ml may impair neuromuscular function.