Recommended Dosage of Mestinon (Pyridostigmine) for Myasthenia Gravis
For myasthenia gravis, pyridostigmine bromide (Mestinon) should be started at 30 mg orally three times a day and gradually increased to a maximum of 120 mg orally four times a day as tolerated and based on symptom response. 1
Dosage Forms and Administration
Immediate-Release Formulation
- Starting dose: 30 mg orally three times daily
- Titration: Gradually increase based on symptom response
- Maximum dose: 120 mg orally four times daily (480 mg total daily dose)
- Dosing interval: Typically every 4-6 hours
Extended-Release Formulation
- Dosage: One to three 180 mg tablets, once or twice daily
- The interval between doses should be at least 6 hours
- The immediate effect of a 180 mg extended-release tablet is approximately equal to a 60 mg immediate-release tablet
- Duration of effectiveness averages 2.5 times that of a 60 mg immediate-release dose 2
Dosing Considerations
- Dosage must be individualized based on patient response and symptom control
- For optimal control, it may be necessary to use the more rapidly acting regular tablets or syrup in conjunction with extended-release therapy 2
- Patients receiving daily doses of pyridostigmine exceeding 300 mg have been found to experience more symptoms of overactive bladder 3
Efficacy and Side Effects
- Pyridostigmine is considered first-line therapy for myasthenia gravis despite limited data from controlled clinical trials 4
- In a cross-sectional study, patients reported a median effectiveness score of 60 (on a scale of 0-100) 5
- 91% of patients using pyridostigmine report side effects, most commonly:
- Gastrointestinal: Flatulence, diarrhea, abdominal cramps
- Urinary: Urgency
- Muscular: Cramps, twitching
- Other: Blurred vision, hyperhidrosis 5
Monitoring and Precautions
- Regular monitoring of symptom response is essential to adjust dosing
- Elderly patients require more cautious dosing due to increased sensitivity to side effects 1
- Rare but serious cardiovascular side effects have been reported, particularly in elderly patients, including myocardial ischemia due to coronary vasogenic spasm 6
- For surgical patients, pyridostigmine should be continued until surgery as it may affect response to neuromuscular blocking agents 1
Combination Therapy
- For patients with Grade 2 symptoms (mild generalized weakness), corticosteroids such as prednisone 0.5-1.5 mg/kg orally daily may be added 1
- For more severe disease, immunosuppressive therapy is often required in addition to pyridostigmine 4
Remember that pyridostigmine provides symptomatic relief but does not alter the underlying disease process. Most patients with moderate to severe myasthenia gravis will eventually require immunosuppressive therapy in addition to pyridostigmine for optimal disease control.