title: 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 concentration of the quaternary amine in plasma was maintained within a relatively narrow range (usually between 20 and 60 ng/ml). In 3 myasthenic patients, the area under the plasma concentration-time curve was relatively constant 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 myasthenic patients. In 1 subject, the bioavailability of the quaternary amine was increased 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 intramuscular administration in a different patient (1.49 hr).
mesh_terms: D000284:Administration, Oral; D000328:Adult; D001682:Biological Availability; D005260:Female; D006207:Half-Life; D006801:Humans; D007273:Injections, Intramuscular; D008297:Male; D008875:Middle Aged; D009157:Myasthenia Gravis / Q000097:blood* / Q000188:drug therapy; D011729:Pyridostigmine Bromide / Q000008:administration & dosage / Q000097:blood* / Q000627:therapeutic use; D013997:Time Factors
chemical_list: D011729:Pyridostigmine Bromide