Mestinon only treats symptoms. One should take the minimum amount necessary to achieve a relative symptom free experience. It may take a bit of trial and error to get the best Mestinon schedule.

Here is a link from an earlier threads about Mestinon:

http://neurotalk.psychcentral.com/showthread.php?t=201455

Mestinon takes effect around one hour after taking a dose and usually continues to lessen symptom for two or three more hours.

I was taking one 180 mg Mestinon Timespan at bed time and three 60 mg Mestinon tablets during the waking hours. The Timespan is very expensive, $240 for 30 tablets. I found this was a waist at bed time because rest lesson symptoms. With the knowledge of my neurologist, I stopped taking the Timespan. Right now I only need one Mestinon tables every now and then, usually late into the day. This, of course, can and probably will change in the future.

Before experimenting with dose and times, be sure to have your sister discuss the issue with her neurologist.

BTW how much experience does your neurologist have with MG patients? You might need to educate your doctors on the finer points of MG. It is so rare that many neurologist lack significant experience treating MG patients.

-Mark-

P.S.: your sister is lucky to have your help.