Reasons for low drug blood levels across all anticonvulsants

[kirsten]

A while back I got blood levels back to find my phenytoin (Dilantin/ Epanutin) levels were subtherapeutic. My valproate levels were also low but accurate in relation to what I was taking. I did blood levels again yesterday and my levels for both have gone down even further.

Some of you explained why phenytoin levels can be irregular and sometimes too low, but now what would cause my levels of both drugs to be consistently moving down? That has to be something that's going wrong with me. So what could it be?

In the past, I've never, ever had a problem with blood levels. Every single drug that had a therapeutic range always did what it was meant to with my blood levels. Always perfect. If there was a blood level competition, I'd have been the gold medalist, based on five years of perfect performance. So something is going wrong. I didn't get to speak to my doc, I just got a worried phone message. We have a long weekend so I'll only be able to speak to a doc on Tuesday and my GP's message left me feeling as though there was a crisis.

 

[kirsten]

I forgot to add that my dosages of valproate and phenytoin haven't changed since the last blood levels.

 

[niceguyVZ]

Hi. I don't have an answer but i just want to say i got blood tested recently because my med not working and the doctor probably wants to check if i have low drug blood levels.

Just wanted to say that. I didn't even know about there being such thing as "low blood levels" but you mentioned it and now i'm aware of it.

 

[Fedup]

kirsten

It could have to do with the level of folic acid in your system or sodium levels, or low blood pressure however the effects of phenytoin on other anticonvulsant medicines, and of other anticonvulsants on phenytoin, are fairly unpredictable. If more than one anticonvulsant is being used at the same time, the blood levels of the medicines, their effect on seizures, and the emergence of side effects should be well monitored. Of course people who take phenytoin long-term may develop vitamin D deficiency. The one thing though is folic acid can also have the opposite effect on the phenytoin and you may have too much of it. There is one other thing once you phenytoin levels incress or decress it is very hard to regulate them to a therapeutic level.

 

[kirsten]

My doctor's been really careful about the Phenytoin issues: I take folic acid and vitamin D, and I have my sodium and electrolyte levels checked every few months. Friday's U and E is normal. I have a heart condition, so I also get monitored for blood pressure changes.

It's possible that the low blood level of phenytoin is causing instability but both drugs? Seems like it must be me and not the drugs. Do you know what I mean?

 

[lindsayschu2]

First, I hate that when they leave a worried sounding message and leave you worried like that--and it often really turns out to be nothing. For example: When you reach your doctor, they could give you a logical explanation for why your level is lower, and the worried tone could just be due to the fact that they want to get the level higher, NOT That there is something inherently wrong with you. My neuro, who granted, is a dumb a$$ (sorry), did say that people's drug metabolism just changes over time, no real explanation sometimes for that. Anyway I would seriously try not to worry because there could be a lot of reasons for it that don't translate to there being something wrong with you, and the tone could just be that they don't want you hanging out with sub-therapeutic levels of meds. Take care of yourself and breathe

 

[Dolores]

Kirsten, I know from experience that Dilantin levels can be affected by other drugs. A google search on Phenytoin & Valproate interactions highlighted this interesting statement

There is a complicated interaction between phenytoin and sodium valproate which displaces phenytoin from protein binding sites and thus changes the therapeutic range, but also inhibits phenytoin metabolism, making difficult to interpret plasma phenytoin concentrations in patients taking valproate.

(Link)

I suggest you talk with your pharmacist & neurologist about the potential interactions between the all drugs you are taking given that your blood levels are no longer in the therapeutic range. No one told me of the interaction with Dilantin when I started taking Zoloft, it was as if the shrink wasn't even aware (sad thing was my GP trusted him to be aware!) In my case, I started to overdose on Dilantin and I had to research it myself to find out why I was suddenly feeling so very odd.

 

[lindsayschu2]

Yes and, when my neuro gave up on me and said he had no idea where to go from here, he said "I don't know, maybe you could try adding a tegretol back in" and that night I had seizures--I talked to my second opinion dr and she said that was a mistake because tegretol metabolizes lamictal and topamax, and lowered my levels of those drugs. Interactions can be tricky.

 

[Cint]

Years ago when I took Dilantin and Tegretol, my levels where low several times. When a person is on more than one med and has several conditions to deal with, they are going to inter-act with each other. Blood levels can change over time.

 

[kirsten]

Thanks for this Delores. It's incredible these days how much research we have to do on behalf of our doctors. Can I just repeat this bit back to you to make sure I understand it. I'm struggling to process the information.

There is a complicated interaction between phenytoin and sodium valproate which displaces phenytoin from protein binding sites and thus changes the therapeutic range, but also inhibits phenytoin metabolism, making difficult to interpret plasma phenytoin concentrations in patients taking valproate.
So phenytoin levels themselves are reduced when taking Valproate, and also, phenytoin blood level readings might be inaccurate when taking valproate, even when phenytoin is in the therapeutic range? So there are two options:
-My phenytoin isn't being absorbed because of the valproate
-my phenytoin is being absorbed properly but my readings are incorrect.

Is that right?

 

[Dolores]

Kirsten, I don't want to pretend to be a pharmacist so I'm not going to attempt to say exactly what the statement means. What I do know is that valproate may have an affect on phenytoin levels. I'm not sure that all people have the same interaction which is why we each must be very aware of what is happening with us as individuals.

For more details I suggest you talk with your pharmacist as they should be aware of the potential interactions.

Also, if you don't already do it, I suggest keeping a log of your dosages and blood levels. For some reason we have not been able to identify, my dilantin levels tend to spike every few years. I finally realize what is happening when I start losing my balance and my brain is in a fog. I'll get a blood test and then, depending on the results, switch to a lower dosage until I can see my doctor. Last time I did this he told me it was exactly what he would have done. We then slowly increased all the time watching my blood levels.

Having the levels & dosage history is wonderful as I can never remember what dosage I was on that had me at what levels.

Hoping you are able to track down the culprits in your own drug level dilemma.
Dolores

 

[kirsten]

Thanks Dolores. I have just started keeping a log of my seizures and levels and meds. I also sent the link you gave me to my doc and asked if it wouldn't be a good idea to cut the epilim. At the moment, having absolutely no AEDs at therapeutic level just seems silly. I'll see what my doc says.

 

[kirsten]

I got my levels. My phenytoin is at 3 and the epilim is at 18. I sent the link to my doc, Dolores, and she's taken me off the epilim as a result, and increased the phenytoin and we're going to check the levels again in a month, so thank you so much for taking the trouble to do that search for me. She says the epilim levels are so low I may as well not even be on it.