Pyridostigmine

INDICATION: MESTINON is useful in the treatment of myasthenia gravis.

ACTIONS: MESTINON inhibits the destruction of acetylcholine by cholinesterase and thereby permits freer transmission of nerve impulses across the neuromuscular junction. Pyridostigmine is an analog of neostigmine (Prostigmin), but differs from it in certain clinically significant respects, for example, pyridostigmine is characterized by a longer duration of action and fewer gastrointestinal side effects.

MESTINON is available in three dosage forms: Oral Solution - raspberry-flavored, containing 60 mg pyridostigmine bromide per teaspoonful (5 mL). This form permits accurate dosage adjustment for children and “brittle” myasthenic patients who require fractions of 60 mg doses. It is more easily swallowed, especially in the morning, by patients with bulbar involvement. Conventional tablets - each containing 60 mg pyridostigmine bromide. TIMESPAN tablets - each containing 180 mg pyridostigmine bromide. This form provides uniformly slow release, hence prolonged duration of drug action, it facilitates control of myasthenic symptoms with fewer individual doses daily. The immediate effect of a 180 mg TIMESPAN tablet is about equal to that of a 60 mg Conventional tablet, however, its duration of effectiveness, although varying in individual patients, averages 2½ times that of a 60 mg dose.

MESTINON is contraindicated in mechanical intestinal or urinary obstruction, and particular caution should be used in its administration to patients with bronchial asthma. Care should be observed in the use of atropine for counteracting side effects, as discussed below.

Although failure of patients to show clinical improvement may reflect underdosage, it can also be indicative of overdosage. As is true of all cholinergic drugs, overdosage of MESTINON may result in cholinergic crisis, a state characterized by increasing muscle weakness which, through involvement of the muscles of respiration, may lead to death. Myasthenic crisis due to an increase in the severity of the disease is also accompanied by extreme muscle weakness, and thus may be difficult to distinguish from cholinergic crisis on a symptomatic basis. Such differentiation is extremely important, since increases in doses of MESTINON or other drugs of this class in the presence of cholinergic crisis or of a refractory or “insensitive” state could have grave consequences.

The side effects of MESTINON are most commonly related to overdosage and generally are of two varieties, muscarinic and nicotinic. Among those in the former group are nausea, vomiting, diarrhea, abdominal cramps, increased peristalsis, increased salivation, increased bronchial secretions, miosis and diaphoresis. Nicotinic side effects are comprised chiefly of muscle cramps, fasciculation and weakness. Muscarinic side effects can usually be counteracted by atropine, but for reasons shown in the preceding section the expedient is not without danger. As with any compound containing the bromide radical, a skin rash may be seen in an occasional patient. Such reactions usually subside promptly upon discontinuance of the medication.

Store MESTINON (pyridostigmine bromide) Oral Solution, USP, MESTINON tablets, and TIMESPAN tablets at 25°C (77°F), excursions permitted to 15° to 30°C (59° to 86°F).