The thing about Mestinon is that it is different for everybody. Typically they prescribe three 60 mg tablets (180 mg a day) not closer that 4 hours apart. I can tolerate much higher doses. When I was in the hospital for my recent MG crises, my neurologist administered a 60 mg dose every 4 hours for 6 days.

The MG Manual has great section on cholinesterase inhibitors:

No fixed dosage schedule suits all patients. The need for cholinesterase inhibitors varies from day to day and during the same day. Different muscles respond differently—with any dose, some muscles get stronger, others do not change and still others become weaker. The drug schedule should be titrated to produce an optimal response in muscles causing the greatest disability.

Myasthenia Gravis: A Manual for the Health Care Provider (PDF) - page 17

-Mark-