We have enough problems with the unpredictability of our disease without having to deal with unpredictability of medications. Although effectiveness of medications like mestinon may depend on our own antibody production, there can be other reasons it and our other medications may be causing problems. Pay attention to storage requirements, some medications have very narrow ones regarding, temperature, light, humidity. The hold of an airplane or in a closed car may not meet those requirements.

Generic substitution may be an acceptable way to save money and afford medication, but once stable on medication you can afford, stay with the same manufacturer and take those medications to the hospital. Although brand to generic substitution may be acceptable generic to generic substitution is not. Many of our drugs have a narrow therapeutic to toxic range and substitution of manufacturers is not allowed--which doesn't mean that it does not occur, not only with mail order pharmacies, but in hospital. If you are not formally admitted to the hospital, you will be charged for medication as an outpatient at hospital rates which is another reason to take your own meds.

This is an excellent explanation which is both reassuring and cautionary regarding generic substitution.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3150029/#!po=4.06977

Small excursions out of storage range may not make your drugs worthless, but holding them in a tight fist or close to your heart, for any length of time may. :-) b.