Ana,

Mestinon is a fast-acting drug. Whatever results it's going to have should show up right away. It doesn't have to build up in your system or anything like that.

Most people with MG are helped by Mestinon, but not all of us.

I hope that you will get a single-fiber EMG next (SFEMG). A lot of us here who have negative blood tests were diagnosed by SFEMG. Also, there are three different kinds of antibodies that they commonly test for (and more that they know about). The most common one is the AChR-antibody, but they should also test you for the MuSK anitbody and for LEMS.

Abby