I have had seizures since 1970, and am presently taking Dilantin, Keppra and Klonopin. I have taken almost every other AED, including several no longer on the market.
I seem to be very sensitive to drug changes. Dilantin is known as a medication that has a wide "bioavailability." That is, different people taking exactly the same brand of medication will need to take different amounts, because their bodies process it differently. This also holds true for different manufacturers. The fillers they put in for processing apparently have at least some effect.
About 2 years ago the original manufacturer of Dilantin Kapseals decided not to manufacture the 100 mg product anymore, and I was forced to change to generic phenytoin-sodium. Fortunately my HMO's pharmacy decided to choose one generic vendor and stick with them. I had about 2 months or so of playing with drug levels until I was stable again. Fortunately, my doctor understands that after this amount of time on meds, I can do a bit of adjusting by myself as I feel side-effects. Fortunately there is also a blood test for serum dilantin, and I basically adjust until my tests show I am in the therapeutic range. Then I tell the doctor what the new adjusted level is. I also take 30 mg name-brand Kapseals (which were not discontinued) and that allows me to tune my serum dilantin level.
I understand that there is a blood test for Keppra level, but that there is no recognized theraputic level. I suggest that anyone having their meds changed get a blood test first (assuming there is one for the specific med) and then after changing, get another test once the new medication has had time to stabilize. If you are going to Keppra generic, you would then want to adjust, with doctor's approval, to get to the same number that was working for you previously.
I was set to go on generic Keppra, and talked my doctor into writing a prescription for the name-brand. She said that she had not heard of any issues in the few weeks that the HMO has been using it, but recognized that I seem to be very sensitive to changes, and together we decided i didn't need to go through the several weeks hassle of changing. Especially because the name-brand was still available.
Just to complete the thoughts, I also had problems with Klonopin, but found a generic that worked the same for me at the same dosage. The pharmacist agreed to special order that brand whenever I brought in my prescription. It took a day or two longer to get the meds, but was a good choice. It may not work for everyone.
Thanks for listening. Good Health.