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HomeAnswersNeurologyphenytoinWhat can be the cause of high Phenytoin level?

What could be the reason for my high Phenytoin level?

The following is an actual conversation between an iCliniq user and a doctor that has been reviewed and published as a Premium Q&A.

Medically reviewed by

iCliniq medical review team

Published At October 28, 2016
Reviewed AtAugust 1, 2023

Patient's Query

Hi doctor,

I am on Phenytoin (Dilantin) 300 mg or 350 mg every alternate days for 4 years and 250 mg and 500 mg Levetiracetam in the morning and evening respectively. I was diagnosed with generalized seizure before 8 years. Then, I had one seizure before 4 years. I am seizure free for up to 4 years now. As part of moving to a new country, I went to the GP to get a neurologist reference and he referred a Phenytoin test before referring to a neurologist. In my Phenytoin blood test, the level of Phenytoin is more than 140. Due to the high level of Phenytoin, the doctor sent me to the emergency where everything came out to be normal. I have no problem in doing any activity. However, numbers are too high to be practical for the doctor. I have been looking online is regarding information about abnormal high Phenytoin level without any conditions like change in medication or pregnancy or other diseases.


Welcome to icliniq.com. I understand your question. Phenytoin level of 140 is really high. In our practice, in such a scenario, we do correlate the laboratory test result with the clinical picture.When the level is really 140, the patient cannot stand steady. He will have a severe imbalance while walking, fluttering eyes, loss of appetite, elevated liver enzymes, etc. From your description what I learnt is that you have no such problems. So,the best thing to do in this scenario is to repeat the Phenytoin levels. I suppose, you already know that you should not give sample while you are taking Phenytoin. There are laboratory instructions which differ from laboratory to laboratory and you need to follow that before giving the sample.Sometimes, the sample given after taking Phenytoin tablet may show high levels. I am sure that your neurologist would also think the same. There are no conditions in which Phenytoin will go so high without changing the dose or pregnancy, etc.

Same symptoms don't mean you have the same problem. Consult a doctor now!

Dr. Hardik Nareshbhai Rajyaguru
Dr. Hardik Nareshbhai Rajyaguru


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