Jump to content
NP Dr. Young

Out of Range Gabapentin Level

Recommended Posts

Hi All

I ordered a gabapentin level from Quest Dx as part of my routine new patient lab orders.  The patient is on 300 mg tid from another provider.  The result came back out of range at 100,000 ng/ml.  The reference range is <1000 ng/ml.   I called the lab to discuss the validity and reliability of the result but have not heard back from them.

My own research suggests that toxicity from gabapentin can occur at much lower levels but that some patients require up to 80,000 ng/ml for relief.  I then called the manufacturer, Amneal, to inquire about expected ranges of levels from various daily doses of gabapentin and was told that they don’t know.

Any thoughts or suggestions?

 

Thank you.

NP Dr. Olivia Young, FPMHNP-BC

Share this post


Link to post
Share on other sites

My sense is that you find the use of high doses of this drug to be problematic. I hope responses to your question also touch on the issue of gabapentin misuse. I have a husband and wife opiate use disorder patients who both take 800 mg tid, which I am in process of reducing. I also understand that there is a demand for this drug among our population struggling with substance abuse disorders, so that diversion in my high dose patients may be a feature of their misuse, as well.

Share this post


Link to post
Share on other sites

Right, the level is problematic for me.  I have never seen a lab level of 100,000 ng/ml before and, at any rate, can't see how 300 mg tid would ever lead to such a range.  The patient is negative for all other drugs.

I'm wondering how others would approach the result.

Share this post


Link to post
Share on other sites

I understand that one can crush and snort gabapentin. I would expect blood concentrations to be much higher with that route of administration than with oral intake. I found some data on gabapentin peak concentrations after administration of single 400mg doses of gabapentin. The mean Cmax was less than 4.0mcg/mL (or 4000ng/mL). You could likely get higher concentrations with higher and repeated dosing, but >100,000ng/mL seems unlikely, especially if there was no renal impairment. My lab told me that if I thought someone was snorting gabapentin, I could do a nasal swab and if any gabapentin was present, that would support intranasal use. I think that may go beyond what I need to know to make clinical decisions. I have never ordered a gabapentin level because they are not known (to the best of my knowledge) to be clinically useful in treatment. I am attaching a couple of articles.

Bockbrader PK PD pregabalin gabapentin Clin PK 2010.pdf

Gidal inter intra subject variability in gabapentin absorp Epi Res 2000.pdf

Share this post


Link to post
Share on other sites
On 9/15/2017 at 2:59 PM, NP Dr. Young said:

Hi All

I ordered a gabapentin level from Quest Dx as part of my routine new patient lab orders.  The patient is on 300 mg tid from another provider.  The result came back out of range at 100,000 ng/ml.  The reference range is <1000 ng/ml.   I called the lab to discuss the validity and reliability of the result but have not heard back from them.

 

My own research suggests that toxicity from gabapentin can occur at much lower levels but that some patients require up to 80,000 ng/ml for relief.  I then called the manufacturer, Amneal, to inquire about expected ranges of levels from various daily doses of gabapentin and was told that they don’t know.

 

Any thoughts or suggestions?

 

 

 

Thank you.

 

NP Dr. Olivia Young, FPMHNP-BC

 

Reference range? that may just mean that they can identify a level as low as that. I regularly use 800 mg TID and will look at the lives I get on those folks but I only limit by side effects such as urinaryretention or changes or peripheral edema- both of which happen occasionally at higher doses. 

You can check his levels yourself and come to see what is " normal" for him.  I am not sure whether there is any literature that speaks to blood level of higher doses but there may be in the study that looked at 1200 mg TID to prevent drinking alcohol.

 

 

Share this post


Link to post
Share on other sites

The patient may have "spiked" his/her urine sample by adding gabapentin directly into the cup. This would explain the supraphysiologic levels. This could also mean that he/she may have diverted gabapentin. Gabapentin has some street value, is abused  and diverted. 

Share this post


Link to post
Share on other sites

I recently have spoken with two patients who report injecting the combo bupe/gaba. It was my first experience hearing a person state they inject the gaba as opposed to snort or take orally in large amounts. Is that a possibility here? 

Share this post


Link to post
Share on other sites

Hello,

This sounds like it may have been a urine gabapentin test (Quest ref range < 1000 ng/mL) versus a serum gabapentin test (result peak ranges 2.7 - 4.1 mcg/mL and 4.0 - 8.5 mcg/mL for single vs multiple doses of 900 - 1800 mg/day). If the urine specimen tested was very concentrated, this would cause a higher ng/mL result.

Unless you're just looking for the unexpected/expected presence of gabapentin, a serum gabapentin test would be the better one to order for a more accurate level.  

I hope this is helpful to someone if not the original poster.

  • Upvote 1

Share this post


Link to post
Share on other sites

Join the conversation

You are posting as a guest. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...