Expert: Sophia, R.N., M.S. - 10/17/2009

Question
QUESTION: I have a question about the levels of Carbatrol. I take 700 mg a day. I have my levels tested every 6 months. The levels for me are best at 8.7 - 9.0. I had surgery and my levels in April 2009 was at 7.3 (had bone surgery and lost a lot of blood) Now I had my levels tested a few days ago. They were 6.0. This is very very low for me. I have not changed any meds or foods. Do you know what would cause this change. I have been on carbatrol for 9 years. No problems. Have you ever seen a drop. If so, why. Thank you so much for your time.

ANSWER: Dear Deb,

To answer your question, yes.  This is fairly common with carbamazepine and some other antiepileptic medications.  There is a change on how you metabolize the drug, and the plasma levels will be lower.  Often it has to do with what other medications you are taking.  Some other medications will react with the carbamazepine and drop the levels.
Deb, you either have to reduce any other meds which may be affecting the carbamazepine, or raise the Carbitrol dose.
Good luck to you.  Write if you have other questions.
Sophia

---------- FOLLOW-UP ----------

QUESTION: I talked with the pharmacist, I only take LISINOPRIL 5mg. The pharmacist said there was no reactions. I am concerned only because know my levels need to be in the 9 - 10 range. We are adding another 200 at night. But it takes so long to get the levels up. Any suggestions? Thank you for all your help. Why the sudden drop, I have never had it drop unless I had surgery. I am so confused. I was doing so well for 5 years.

Answer
Deb,
Sometimes plasma levels of drugs are not consistent even with the same dose without any apparent cause. This effect is very common with phenytoin but is also seen with carbamazepine.  I don't know why this happens.  You say that your dose was increased another 200mg.  This should increase your plasma level sufficiently.  Please have your level taken 1-2 weeks after taking the increased dose to assure that you are not in a toxic range.  Deb, you did not say if you are seizure free on your medication.  If you have been seizure free for 1-2 years, you may want to try to taper the drug under EEG monitoring conditions to see how you do with a low dose or no meds.  
I am certain that your plasma level will stabilize again.
Good luck with all of this Deb.
Regards,
Sophia