Plasma pyridostigmine levels in patients with myasthenia gravis

Abstract

Plasma concentrations of pyridostigmine were measured in 7 patients with myasthenia gravis. Six subjects on oral pyridostigmine bromide were stabilized on widely different doses of the drug (60 to 660 mg/day). Nevertheless, the eoneentration of the quaternary amine in plasma was maintained within a relativeiy narrow range (usually between 20 and 60 ng/ml). In 3 myasthenic patients, the area under the plasma concentration‐time curve was relatively eonstant for 4 hr after the same oral dose of pyridostigmine (60 mg). Despite this similarity, there were in general considerable interindividual differences in the bioavailability of pyridostigmine in myasthenie patients. In 1 subject, the bioavailability of the quaternary amine was inereased sixfold by doubling the oral dose from 30 mg to 60 mg. After oral administration of pyridostigmine, the half‐life of the drug in one subject (4.25 hr) was almost three times as great as after intramuseular administration in a different patient (1.49 hr).