Author(s): Anita Kishore; Linda King

Gabapentin (Neurontin) is now widely used for neuropathic pain. Controlled clinical trials in diabetic neuropathy and postherpetic neuralgia show that gabapentin at 2400-3600 mg/day has an efficacy similar to the tricyclic antidepressants. Consistent, though less compelling clinical evidence supports its use for a variety of other neuropathic pain syndromes, including cancer pain syndromes, pain associated with HIV infection, chronic back pain and others. The exact mechanism and site of action of gabapentin is unknown. Its use for neuropathic pain has become widespread because it is generally well-tolerated, easily titrated, has few drug interactions, and does not require laboratory monitoring. However, cost may be a limiting factor for some patients.

Patients suitable for Neurontin should ideally have a clear neuropathic pain syndrome, characterized by sharp, shooting, lancinating and/or burning pain, in a nerve root (radicular) or stocking/glove distribution.

Adult Dosing

Gabapentin is started at low doses (100 mg QD to 100 mg TID) and increased by 100 - 300 mg every 1-3 days to effect (a typical schedule might include: Day 1: 300 QHS; Day 3: 300 mg BID; Day 5: 600 mg BID, Day 7: 600 mg TID). The usual effective total daily dose is 900-3600 mg, administered in three divided doses per day; higher doses may be needed. Titration should proceed more slowly in elderly patients.

Dosing in Renal Failure

Gabapentin doses must be reduced for patients with renal insufficiency.

CrCl (Creat. Clear.) 30-60: max dose 300 mg PO BID;

CrCl 15-30: max dose 300 mg PO QD;

CrCl < 15: max 300 mg PO QOD. For patients on hemodialysis: max 200-300mg dose only after each dialysis session.

Adverse Reactions

Sedation and confusion, as well as dizziness and ataxia, are the most common side effects, especially with rapid dose titration. Tolerance to these effects appears to develop within a few days if the dose is held at the highest tolerated dose until symptoms improve or stabilize.

Dosage Formulations

Neurontin is available in 100 mg, 300 mg, and 400 mg capsules, 600 mg and 800 mg tablets, and as a liquid (250mg/5mL).

Cost

Neurontin is more expensive ($100-$200 per month) than other agents used for neuropathic pain (tricyclic antidepressants and older anti-epileptic drugs such as carbamazepine). An indigent drug program is available from the manufacturer.

Summary

Gabapentin is a safe and effective adjuvant analgesic for neuropathic pain. Physicians should become comfortable using and titrating gabapentin in patients with neuropathic pain syndromes.

References

American Pain Society. Principles of Analgesic Use in the Treatment of Acute Pain and Cancer Pain. 1999.

Backonja M, Beydoun A, Edwards KR, Schwartz SL, Fonseca V, Hes M, LaMoreaux L, Garafalo E. Gabapentin for the symtomatic treatment of painful neuropathy in patients with diabetes mellitus: A randomized controlled trial. JAMA 1998; 280: 1831-1836

Rowbotham M, Harden N, Stacey B, Bernstein P, Magnus-Miller L. Gabapentin for the treatment of postherpetic neuralgia: A randomized controlled trial. JAMA 1998; 280: 1837-1842.

Adapted from: Emanuel, LL, von Gunten, CF, Ferris, FF (eds.). Module 4: Pain Management. The EPEC Curriculum: Education for Physicians on End-of-life Care. www.EPEC.net: The EPEC Project, 1999.

Copyright Notice: Users are free to download and distribute Fast Facts for educational purposes only. Citation for referencing. Fast Fact and Concept #49 Kishore A and King L. Gapapentin for neuropathic pain. September, 2001. End-of-Life Physician Education Resource Center www.eperc.mcw.edu.