Mestinon® is an orally ingested cholinesterase inhibitor used as the first source of therapy in treating MG. Acetylcholine is a chemical, one of the main neurotransmitters in the brain that sends nerve impulses to the skeletal (voluntary) muscles. With MG, there is a breakdown of acetylcholine in the neuromuscular 
receptor sites, responsible for voluntary muscle control. Mestinon® prevents this breakdown of acetylcholine by allow- ing more acetylcholine to accumulate at the neuromuscular receptor sites, providing more control of voluntary muscle function, such as eye movement, limited strength, swallowing, chewing and breathing.
The physician determines the amount of Mestinon® dose and frequency according to the needs of each individual patient. During the initial induction of Mestinon®, the patient should keep a record reflecting the responses of symptoms after each dose. This helps the physician deter- mine the correct dose and frequency for the patient, especially when the patient’s MG is unstable.
It is very important to follow the physician’s instructions pertaining to the patient’s Mestinon® dose and frequency. Discuss any change made in your Mestinon® regimen with your physician because too much Mesti- non® can induce extreme muscle weakness.
Equally important, discuss any instability of Myasthenia Gravis weakness with the physician BEFORE chang- ing the initially prescribed dose and/or frequency.
PRECAUTIONS AND SIDE EFFECTS
Precaution should be taken in patients with mechanical intestinal and urinary obstruction. Particular precau- tion should be taken when administering Mestinon® to patients with bronchial asthma.
The most common side effects of Mestinon® include nausea, vomiting, diarrhea, abdominal cramps, in- creased tearing, salivation and bronchial secretions. Other side effects are muscle twitching, muscle cramps and weakness.
Since Mestinon® is eliminated from the body mainly unchanged by the kidneys; lower doses may be required in patients with renal (kidney) disease. The safety of Mestinon® has not been established during pregnancy and lactation, or in pediatric patients. When taking Mestinon®, failure of improvement of symptoms may be a sign of overdose or underdose.
Note: During the Gulf War, pyridostigmine bromide tablets were administered to the military as a form of pro- phylaxis against the lethal effects of soman nerve agent poisoning.
THREE FORMS OF MESTINON®
1. The conventional 60 mg tablets contain pyridostigmine bromide, as well as lactose, silicon dioxide and stearic acid.
2. Mestinon Syrup® contains 60mg of pyridostigmine bromide. Also included are 5% alcohol, glycerin, lactic acid, sodium benzoate, sorbital, sucrose, FD&C red # 40, FD&C blue # 1, flavors and water. The syrup is raspberry flavored. This formula allows dosage that is more precise for children and people with ‘brittle’ or fragile MG who may require doses in fractions of the 60mg. It is also more easily swallowed by patients with swallowing difficulties in the morning.
3. Mestinon Timespan® tablets contain 60mg of pyridostigmine bromide as well as carnauba wax, corn- derived proteins, magnesium stearate, tribasic calcium phosphate and silica gel. Mestinon Timespan® talblets are the slow-release dosage form. They should not be crushed or broken into pieces as this disturbs the time-release mechanism and could result in IMMEDIATE release instead of slow release of pyridostigmine bromide.
PROPER STORAGE OF MESTINON®
Mestinon® tablets and Mestinon Timespan® tablets are hygroscopic, meaning they pick up and retain moisture. Mestinon® tablets that are exposed to moisture may appear mottled or discolored, and easily crumble. Though moisture affects the appearance of the tablets, it does not alter the drug’s efficiency.
Do not store Mestinon® tablets and Mestinon Timespan® tablets in a bathroom or kitchen where humidity may be a factor.
Mestinon® tablets are packaged in a bottle of 100 or 500 tablets whereas Mestinon Timespan® tablets are packaged in bottles of 30 tablets.
Myasthenia Gravis Association of British Columbia 