Your doctor will also consider how the medications may affect you. People react individually to medicines just as they do to other substances that enter the body, and one person may experience side effects while another may not. What all this means is that doctors may have to try several medications to find one that is effective for you. With so much variability among people, it may also take some time to customize the dosage of medication. One of the ways your physician determines how much medication you need to take is to measure how much of it is present in your blood.
Some medicines reach an effective, seizure-preventing level in the blood more quickly than others.
Knowing how much medication is in your blood shows how much medication is getting up to your brain, where seizures occur. If seizures are not controlled and the level is low, the dose of medication may have to be increased. If the level is too high, side effects are more common and the dose may be reduced.