Gabapentin Dose Dependent Absorption – Treating Neuropathy

A huge challenge in clinical pharmacy is determining what information is actually relevant.  By relevant, I mean what information actually impacts patient care.

I see gabapentin most frequently used for neuropathy.  The pharmacokinetics of gabapentin are a little unique in that gabapentin has an inverse dose dependent absorption.  What does this mean?

This means that as you increase the dose, you actually get less (percentage) of the medication absorbed.  Clinically this means that as you get to higher doses, you may not get as great of an anticipated response in neuropathy treatment given an increase in dose.

Why does this happen?  Gabapentin requires a transporter to get across the GI tract.  As the dose increases, this transporter gets “saturated” with drug.  It can’t get all that drug transported across before it moves further down the gut.  Think about one lane on a busy New York City bridge, if only a few cars are there, a higher percentage will get through.  If a lot of cars are there, less will get through.

From Lexi-comp, here are the bioavailability numbers:

  • 900mg/day 60% is absorbed
  • 1,200 mg/day 47% is absorbed
  • 2,400 mg/day 34% is absorbed

Doing the math here on how much is actually absorbed

  • 900X0.6 = 540mg
  • 1,200X0.47 = 564mg
  • 2,400X0.34 = 816mg

Always keep in mind that these are approximations, but I think these numbers demonstrate what I’m talking about.  So if you see someone already on moderate to high doses, and continue to push the dose, a 100 mg increase at low dose will likely cause more of a response than a 100 mg increase at higher doses.  Also remember that once absorbed, the kidneys come into play which can change the game again 🙂

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8 Comments

  1. Julia Grunbaum

    Eric, a lot of Gabapentin is used for neuropathic pain in adolescents. Your information is really interestint! Please, coul you post bibliography about this subject? Thank you very much!

    Reply
  2. Alka Bhalla

    Hi Eric,
    Thank you for posting this! It refreshed my memory again – I haven’t rechecked but I believe pregabalin follows linear kinetics. Any thoughts on how to convert between mg gabapentin and mg pregabalin.
    Alka

    Reply
    • Eric Christianson

      pregabalin does avoid this phenomena, but is pretty expensive still (at this time)…I can’t imagine many scenarios in which I would try to convert gabapentin to pregabalin without doing some sort of cross tapering; but starting dose and how quickly you’d taper would depend on multiple factors…Good question – Eric

      Reply
  3. ahmed

    thank you

    Reply
  4. Matt Zimmerman, Pharm.D., MHA, CMTM

    Thanks for the post Eric. Great insight into PK and Dosing of gabapentin. I see it’s part of your MED ED 101. I think I can learn alot from you. Much appreciated. Keep up the great consult work.

    Reply
    • Eric Christianson

      Thanks so much!!!

      Reply

Trackbacks/Pingbacks

  1. Gabapentin Versus Pregabalin - Med Ed 101 - […] after about 3-4 hours. It also displays saturable absorption, which can lead to unpredictable kinetics (here’s what that means…
  2. RLS Guidelines Change and Clinical Pearls - Med Ed 101 - […] Remember the dose-dependent absorption issue with gabapentin. As you get to higher dosages, there is the potential that you…
  3. Gabapentin and Renal Function - Case Scenario - Med Ed 101 - […] Here’s another clinical pearl regarding gabapentin effectiveness and how this drug’s absorption can vary based upon the dose. […]

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Written By Eric Christianson

May 10, 2015

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