How Long Until Seizure Medicine Works?
How Long Does It Take for Seizure Medicines to Reach the Bloodstream?
A dose of medication will reach a peak, or maximum, level in the blood 30 minutes to 4 or 6 hours after it is taken. The time between taking the medication and reaching the peak level depends on the specific medicine and what form it is in, for example a liquid, tablets, capsule or slow-release form. Eating before a dose may also affect how long it takes to reach a peak level.
- In general, liquids are absorbed quickly.
- Medications in slow-release forms are absorbed gradually over hours and produce the steadiest levels in the blood. These slow-release forms can be taken less often, once or twice a day.
What Does "Half-Life" Mean?
A medicine's half-life is the time it takes for its level in the blood to be reduced by one-half. The half-life of each seizure medicine depends on how quickly it is broken down and gotten rid of from the body. How often a medicine should be taken depends on the drug’s half-life.
- If a medicine has a short half-life, the amount in your blood may quickly become too low to control your seizures. Medicines with short half-lives ideally should be taken several times a day. Then you can take a smaller amount each time and your blood level will stay more stable.
- Medicines with long half-lives have more stable levels over a number of hours. This lets the medicine be taken less often.
The speed at which your body (typically the liver, or in some cases, kidney) gets rid of many medicines will vary somewhat between individuals. Also, as we get older, this speed tends to slow down. This is one reason why drug doses may vary between patients, and why prescribed drug doses may change over time.
When Are Seizure Medicines Most Likely to Work?
Seizure medicines work best when the amount in your system reaches a steady state or constant amount.
- To keep this steady or constant amount, the medicine needs to be taken on a regular basis. The amount you take in needs to equal the amount your body gets rid of.
- Just because a medicine has reached a steady state doesn’t mean that it will control seizures. Only by taking the medicine for a while (usually at least a few weeks) can you tell if the drug is going to work for you.
Is It Normal for Blood Levels of Seizure Medicines to Fluctuate?
Yes, even when someone has been taking the same medication for a long time the measured blood level may vary a bit during the day. To help your healthcare provider understand these fluctuations, it is important to let them know when you last took medicine before your blood test. You should also let them know if you have missed any doses within the 1-2 days prior.
Dose-related side effects are more likely to occur at times of the highest (peak) levels, and a seizure is more likely to occur at times of the lowest (trough) levels.
Learn More:
Find Your Local Epilepsy FoundationResources
Epilepsy Centers
Epilepsy centers provide you with a team of specialists to help you diagnose your epilepsy and explore treatment options.
Epilepsy Medication
Find in-depth information on anti-seizure medications so you know what to ask your doctor.
Epilepsy and Seizures Helpline
Call our Epilepsy and Seizures Helpline and talk with an epilepsy information specialist or submit a question online.
Tools & Resources
Get information, tips, and more to help you manage your epilepsy.
Related Stories
Press Releases
Epilepsy Foundation of America’s National Walk for Epilepsy Set to Return to Washington D.C.
Read Story
