I take 3000mg/day of Gabapentin for chronic pain from peripheral 
neuropathy (i.e. not seizure disorder). This is a very large dose.  What 
significant side effects are there at this high dosage, aside from 
somnolence?  What can I do to monitor, alleviate or prevent side effects?   
Any blood or urine tests to monitor usage?  If I have surgery is this high 
dosage a problem?

Hello and thank you for your question:

The good news is that studies do show Gabapentin as effective against
neuropathic pain, and it's side effects generally are not serious:
"A recent article in the Southern Medical Journal discusses anecdotal
evidence that antiseizure drugs provide the best relief for
neuropathic pain, associated with nerve problems. The newest and most
successful has been gabapentin, which seems to relieve a wide range of
nerve pain, including that often accompanying cancer and aids. Better
yet, this class of drugs has a low level of side effects. Drowsiness,
dizziness, nausea and unsteadiness, if they do occur, can usually be
alleviated by adjusting the dosages of the drug, while more severe
side effects, such as liver toxicity, blood disorders and disturbed
vision, are relatively rare."
 Time Magazine--Your Health--October 11, 1999
http://tinyurl.com/i4s

This excerpt also implies that you probably do not need blood or liver
tests to monitor the drug, as long as you remain alert to drowsiness,
dizziness, etc.

These are not the only side effects that you'll find mentioned on the
warning label. Of the following cautions about Gabapentin (Neurontin)
that I found on the Medline information site, it seems that the most
serious likely risk is loss of balance and eye control, so you
shouldn't drive or operate machinery while taking it.

Here are the cautions, organized according to how dangerous they are
to your health, and also by how likely you are to encounter the
effects:

-More Common Side Effects Requiring Medical Attention-
   "Clumsiness or unsteadiness; continuous, uncontrolled,
back-and-forth and/or rolling eye movements"

-Less Common Side Effects Requiring Medical Attention-
  "Depression, irritability, or other mood or mental changes; loss of
memory"

-Rare Side Effects Requiring Medical Attention-
   "Cough or hoarseness; fever or chills; lower back or side pain;
painful or difficult urination"

-Symptoms of overdose-
  "Diarrhea; double vision; drowsiness; sluggishness; slurred speech"

-Other Side Effects That Usually Do Not Need Medical Attention-
   More Common
        "Blurred or double vision; dizziness; drowsiness; muscle ache
or pain; swelling of hands, feet, or lower legs; trembling or shaking;
unusual tiredness or weakness"
   Less common
        "Back pain; constipation; decrease in sexual desire or
ability; diarrhea; dryness of mouth or throat; frequent urination;
headache; indigestion; low blood pressure; nausea; noise in ears;
runny nose; slurred speech; trouble in sleeping; trouble in thinking;
twitching; vomiting; weakness or loss of strength; weight gain"

 [Side Effects of Gabapentin]
http://www.nlm.nih.gov/medlineplus/druginfo/gabapentinsystemic202732.html#SXX18

You are right about 3,000 mg being a high dosage.  One site cautions
that if 600 mg fails to relieve pain, the drug should be discontinued
altogether.
 University Center for Pain Medicine and Rehabilitation at
Memorial/Hermann
http://www.uth.tmc.edu/pain/pl-gaba.html

But pain.com suggests dosages up to 2,400 mg daily for treatment of
migraine.
  Pain.com
http://www.pain.com/freecme/damtm_migraine/damtm_s23.cfm

And dosages of even 5,000 mg are not unheard of:
"The total daily dose of gabapentin may be as high as 5,000 mg if
lower doses are not beneficial. Using this protocol, most patients are
dramatically improved in one or two office visits."
  New Patient Treatment Protocol
http://www.drjgoldstein.com/methodology/protocol.html

So even if you do persist in taking the medication at your current
dosage level, it seems that blood and liver function tests are not
specifically recommended.  Of course, you and your doctor may come to
a different conclusion.

Anther useful link:
 The Pains Of Trigeminal Neuralgia
(This article also mentions surgery, so apparently the drug is not
inconsistent with a surgical procedure)
http://www.personalmd.com/news/trigeminalneuralgia_1211000.shtml

Search Terms Used:
Gabapentin pain liver blood
Gabapentin pain dosage
Neurontin "blood test"
Gabapentin pain dosage

Although I am not a doctor (and you should certainly not rely on this
answer in formulating your treatment plan), I hope you find this
information useful and responsive to your question.  If you need
anything further, I would appreciate your making a request for
clarification before you rate my answer.

Your friend
richard-ga

Dear Richard:  Thanks for your thorough research.  Very helpful and
extremely rapid reply.  renoir-ga

This question has been addressed very well, but I thought I'd add what
I've found about the dosage:
"Antiepileptics are also helpful in the treatment of neuropathic
pain.15 Carbamazepine (Tegretol) has a well established efficacy in
the management of trigeminal neuralgia, and case reports show a
positive effect on neuropathic pain.16 The most effective
antiepileptic medication, gabapentin (Neurontin), has demonstrated
efficacy in reducing pain from moderate to mild in patients with
diabetic neuropathy (900 to 3,600 mg three times a day)17 and in
postherpetic neuralgia (2,400 to 3,600 mg three times a day).18
Patients should expect to experience benefit from a daily dosage of
1,800 mg of gabapentin. If this dose has no effect on the pain, a
higher dose will generally not be helpful. If some relief is
experienced at this dose, a higher dose may further improve pain
relief. Lamotrigine (Lamictal) has been reported to reduce neuropathic
pain in case reports, but controlled studies are not yet available.19"
source: Treatment of Nonmalignant Chronic Pain
http://www.aafp.org/afp/20000301/1331.html

You didn't say how long you've been on this med, but side effects tend
to be dose-related and usually subside within 8 weeks of treatment or
increment.

There is something I recall reading about Neurontin a while back and
I'm not able to find the reference, but it relates to your high
dosage. Something about the bioavailability of the drug and the
incremental dosage...something to the effect that if you double a dose
from 300 to 600, the bioavailability doesn't double and that the
bioavailable dose may be considerably less than the 600, yet slightly
more than the 300. I will continue to find this reference material.

You can read the patient FAQ on Gabapentin (Neurontin) at rxlist.com
http://www.rxlist.com/frame/display.cgi?drug=NEURONTIN

You can read about warnings on Neurontin, including blood level
monitoring information at rxlist.com
http://www.rxlist.com/cgi/generic/gabapent_wcp.htm

You can get information and feedback from others who have used this
med for chronic pain at this fibromyalgia support medical forum:
http://fibrohugsforums.mysitemain.com/cgi-bin/webbbs/fms/index.pl?

Hope this helps 
DuckyMB

Okay, I found some info on the bioavailability and high dosage issue.

"saturable absorption (ca. 60% bioavailable, normally, but can
decrease to 24% with large doses or use of antacids)" source:
http://131.183.68.170/3720/3720_6.html

From the FDA website: "A 400-mg dose, for example, is about 25% less
bioavailable than..."  www.fda.gov/ohrms/dockets/dailys/
00/Jul00/072100/cp00001.pdf

From Pfizer: "Gabapentin bioavailability is not dose proportional..."
www.pfizer.com/hml/pi's/neurontinpi.pdf 

By the way, one of the side effects of this med is possible weight
gain. If this is a great concern to you, there are other meds like
Topomax which might be helpful that you might want to discuss with
your medical team.

Happy reading!
DuckyMB

Info for other chronic pain readers:  Prior to taking the high dose of
Gabapentin my MD suggested Trileptal.  I discontinued this after only
3 days, due to terrible headaches.  I located the mfgrs. report on the
clinical trials for this drug and per their own data, 20 PERCENT of
the patients in the clinical trial stopped Trileptal due to headache. 
I then tried Carbatrol (extended release Tegretol).  it is more
effective than the Gabapentin and much, much cheaper.  But this too
caused headaches and I had to discontinue that also. My MD tells me
that he has 60-70 patients on Carbatrol and they don't have headaches.
 One lesson from all this is that
everyone has a unique physico-chemical system, and some
experimentation is necessary when dealing with chronic pain. renoir-ga

As an FYI, Pfizer recently was granted approval by the FDA to market
Gabapentin for treatment of post-herpetic neuralgia.  Here is a link
(via make a shorter link redriction) and additional information on
neuropathic pain.

http://makeashorterlink.com/?S62753821
http://makeashorterlink.com/?M46721821

Regards,
V