The purpose of this study is to determine whether gabapentin is efficacious as an analgesic
for chronic low back pain.
Chronic low back pain (CLBP) is a major health problem for the VA, affecting up to 15% of
all veterans. Nationally, its medical and disability costs exceed $50 billion annually.
Despite its impact, relatively little research evaluates treatment for CLBP. Wide variation
in patterns of care suggests uncertainty over effective therapy. Most chronic back cases are
not surgical candidates. The mainstays of medical treatment have been non-steroidal
anti-inflammatory drugs (NSAIDs), muscle relaxants, opioids, and antidepressants.
Non-steroidals and muscle relaxants are effective for acute but not for chronic back pain.
Opioids may provide analgesia but safety and stigma limit their use. Tricyclic
antidepressants provide modest pain relief, separate from effects on depression. But it is
clear additional research is needed to develop more effective pharmacotherapy. One approach
favored by many authorities is determining if agents effective for one type of chronic pain
syndrome (e.g., diabetic neuropathy) can be generalized to other syndromes, like chronic
back pain. Another is to identify effective drug combinations, based on selecting drugs with
differing therapeutic mechanisms.
This research is a program of rigorous randomized clinical trials testing the efficacy of
antidepressants for analgesia in chronic back pain. Because chronic pain is a complex
disorder, the program features a multidisciplinary research team, involving specialists in
psychiatry, orthopedic surgery, psychology, anesthesiology, clinical pharmacology, and
biomathematics. The research has both pragmatic and explanatory aims. Our strategy has been
to test antidepressants with differing, and selective properties in an attempt to isolate
therapeutic mechanisms. Thus, we began with trials using selective norepinephrine reuptake
inhibitors, and selective serotonin reuptake inhibitors (SSRIs), rather than those with dual
noradrenergic and serotonergic effects (e.g., amitriptyline, imipramine). To ensure
applicability of results, we have used rigorous diagnostic procedures to identify patients
with chronic back pain due to degenerative disk disease. To enhance generalizability we
recruit primary care patients rather than tertiary pain clinic samples. Patients without
major depression are studied to examine analgesia separate from antidepressant effects.
Secondary outcomes address function and life quality.
We have conducted three controlled trials using identical recruitment and assessment
methodology. The first, comparing a noradrenergic antidepressant (nortriptyline) with
placebo, indicated that the noradrenergic agent provided clinically relevant analgesia. The
second was a head-to-head comparison of a selective noradrenergic agent (maprotiline) with a
selective serotonin reuptake inhibitor (SSRI, paroxetine). The noradrenergic agent
outperformed the SSRI, which was equivalent to placebo. To clarify these results we explored
whether efficacy might be evident only at specific drug concentrations. Therefore, the third
study, has a prospective concentration design comparing the most potent and selective
noradrenergic antidepressant (desipramine) to the standard SSRI, fluoxetine. Subjects were
randomized to placebo or predetermined concentration windows reflecting low, medium, and
high exposure to study drugs and followed for 12 weeks. Interim analysis suggests that low
concentration desipramine outperforms placebo (p<0.05). It is also superior to
mid-concentration and high exposure desipramine--as well as all exposure levels of the SSRI,
which are equivalent to placebo.
In sum, all three studies supported noradrenergic analgesia in CLBP, and the two studies
that evaluated SSRIs failed to find analgesia. This suggests noradrenergic activity,
perhaps within a therapeutic window, may be primarily responsible for back pain analgesia.
These findings have led us away from studies proposing combining noradrenergic and
serotonergic agents. An alternative approach which builds on these data, but first employs
another class of agents, seems reasonable. This strategy is to assess if gabapentin, a
calcium channel blocker agent with demonstrated efficacy in neuropathic pain, can be
extended to chronic back pain.
We propose a double-blind, randomized assignment, 12-week, placebo controlled clinical trial
of the efficacy of gabapentin. Non-depressed chronic low back pain patients (N = 130) will
be randomized to placebo or high dose gabapentin (3600 mg/day or maximum tolerable dose).
Analysis is by intent to treat. The primary efficacy assessment is mean pain intensity
(Descriptor Differential Scale) at exit. Secondary outcomes are function and life quality
(Oswestry Disability Index, SF-36, Quality of Well-Being). Safety evaluation includes rating
adverse events (UKU Side Effects Rating Scale), standardized physical examination, and
clinical laboratory testing. Results could provide explanatory insight into mechanisms of
back pain, and address the pragmatic clinical need by primary care providers and others for
- Must be resident of the county of San Diego, CA
- Ages 21-70 inclusive
- Low back pain (T-6 or below, secondary to degenerative disk or degenerative joint
disease) present "on a daily basis" for the previous 6 months or longer, of at least
"moderate" intensity determined by DDS (Descriptor Differential Scale) > 7
- English-speaking, literate, able to understand the study and communicate with the
- Presently not a candidate for back surgery (one prior back surgery permitted if it
was > 5 years ago and resulted in complete relief)
- Discontinued muscle relaxants, anticonvulsants, antidepressants, and opioids at least
two weeks before screening and agree to discontinue throughout study (can remain on
stable dose of NSAIDs)
- If female, not pregnant or lactating; agrees to use reliable contraception throughout
the study, and has negative pregnancy test at screening
- Gives informed consent.
- A major coexisting medical illness (e.g., diabetes, renal or hepatic disease, chronic
obstructive pulmonary disease, cancer, or class III or IV organic heart disease) that
might increase risks of gabapentin, or major surgical or non-surgical intervention
for any disorder within the past 12 months, since rehabilitation from treatment may
confound study outcomes
- Significant coexisting orthopedic or pain problems; sciatica (pain, weakness, or
dysesthesia solely in distribution of a lumbar spinal nerve, with or without reflex
change) or back pain due to other disorders (e.g., fibromyalgia, vertebral fracture,
osteomyelitis, metastatic cancer, rheumatoid arthritis; spinal stenosis)
- DSM-IV diagnosis of alcohol or other substance abuse or dependence (within the
previous 12 months or positive urine toxicology at screening), current major
depression or dysthymia; or lifetime bipolar disorder (I or II) (excluded because
gabapentin is antidepressive and antimanic); or major anxiety disorder (e.g., panic
disorder; or psychosis; or lifetime presence of cognitive impairment disorder (e.g.
- History of multiple adverse drug reactions or known allergy to gabapentin
- Use of psychotropics (e.g., antidepressants, anxiolytics), which would need to be
continued during the study, or other drugs or agents (i.e., herbal preparations)
which might interact with the study drug
- Prior treatment with the study drug
- Use of systemic corticosteroids or corticosteroid injections within three months of
screening; or concurrent behavioral therapies, chiropractic treatment, or
transcutaneous electrical nerve stimulation unit
- Renal impairment (creatinine > 1.8 mg/dL)
- Hepatic impairment (bilirubin > 1.5 X upper normal limit, or AST or ALT > 2 X upper
- Hematologic abnormality (hemoglobin < 9.4 gm/dL; absolute WBC count < 3000/mm3,
platelets < 100,000
- Use of experimental drugs or participation in other clinical trials