Importance:
1.
Gabapentin is commonly prescribed in our pain clinics because of its relatively favourable drug profile and relatively few side effects.
2.
The cost of gabapentin is ever increasing. We have the responsibility to use gabapentin effectively.
3.
This guidelines for prescribing gabapentin are meant for reference only.
A. Painful sensory neuropathy:
-Monotherapy generally decrease 30-50% in pain at best  multidrug regime recommended
-Try maximum recommended dose, then add 2 nd line drug
1 st line: TCA (tertiary TCA> secondary TCA> SSRI)
2 nd line: gabapentin
3 rd line: tramadol
4 th line: opioid other: carbamazepine, lamotrigine
-exceptions:
Trigeminal neuralgia: 1 st line: carbamzepine, phenytoin, lamotrigine, baclofen
Chronic radicular low back pain: 1 st line: nortriptyline
Contraindications of TCA:
1.
Arrthymia: long QT syndrome, significant conduction system
( bifascicular block, trifasicular block), frequent premature ventricular contraction, sustained ventricular arrthymia
2.
Recent MI (<6/12), unstable angina
3.
Congestive heart failure
4.
orthrostatic hypotension
5.
urinary tract obstruction
6.
narrow-angle glaucoma
7.
> 65 years old (relative CI)

Contraindications of gabapentin:
1.
allergy to gabapentin
2.
pregnancy
3.
previous analgesic failure with gabapentin trial (relative)
4.
history of renal transplant (relative)
5.
myasthenia gravis (relative)
Interaction of gabapentin:
Avoid prescribing gabapentin with:
1.
cimetidine (decrease clearance of gabapentin by reducing glomerular filtration rate)
2.
antacid (reduces the bioavailability of gabapentin by 20%)
Evidence:
In summary, gabapentin is not superior to TCA in terms of efficacy.
Gabapentin is shown to be effective in RCT in neuropathic pain syndrome:
1.
Diabetic neuropathy-
NNT: gabapentin=3.8, TCA=2.4, carbamazepine=2.3, phenytoin
=2.1
NNH: gabapentin=2.6, TCA=3.2 (mild adverse effect e.g. dry mouth, constipation, blurred vision), 17 (severe side effect that patient withdraw from study), carbamazepine NA, phenytoin 3.2
2.
Postherpetic neuralgia- NNT: gabapentn=3.2, TCA=2.3, carbamazepine=2.5
3.
Painful polyneuropathy-NNT: gabapentin =3.7, TCA=2.4, carbamazepine=3.3, phenytoin=2.1
4.
Spinal cord injury: gabapentin effective in RCT
5.
chronic radicular low back pain: gabapentin and nortriptyline effective in RCT
6.
neuropathic pain in malignancy: gabapentin- nonblinded trials only, Cochrane data: gabapentin not superior to carbamazepine
7.
complex regional pain syndrome: amitryptyline 67% effective, gabapentin- nonblinded trials only
8.
trigeminal neuralgia: no RCT on gabapentin, NNT: carbamazepine=2.6
9.
peripheral nerve injury: no RCT on gabapentin, NNT: TCA=2.5
10.
multiple sclerosis: no RCT on gabapentin
11.
HIV neuropathy- no RCT on gabapentin

B. Other painful conditions:
1.
Headache: prophylaxis of migraine- gabapentn effective in RCT
2.
Myofascial pain (2 nd line: TCA/ gabapentin)-no RCT on gabapentin
3.
Interstitial cystitis (3 rd line TCA/ gabapentin)-no RCT on gabapentin
4.
Others: no RCT on gabapentin: Erythromelagia, postpoliomyelitis pain, muscle cramps hemifacial spasm, vulvodynia, anaesthesia dolorosa and dysesthetic pain after reconstructive surgery, postthoracotomy neuropathy and taxane-induced myalgia
12.
central pain syndrome: gabapentin not statistically effective, NNT:
TCA=1.7, carbamazepine=3.4
1.
Review nature of pain syndrome, contraindication, previous drug history and potential interaction.
2.
Prescribe 300mg nocte on D1-3, 300 mg bd on D4-6, 300mg tds on
D7-D9, 600mg tds from D10 till fu in week 3.
3.
Book medication review in week 3.
4.
Patient is instructed on maintaining the current dosage if analgesia is satisfactory, increasing the dosage accordingly if analgesia is inadequate or reducing the dosage accordingly if intolerable side effects. An information sheet on gabapentin trial is given to the patient.
5.
Patients are reviewed on efficacy of gabapentin trial and further dosage adjustment is considered.
Reference:
1.
M.A. Rose, P.C.A. Kam: Gabapentin: pharmacology and its use in pain management. Anaesthesia 2002; 451-462
2.
Jianren Mao, Lucy L. Chen: Gabapentin in Pain management.
Anesth Analg 2000; 91: 680-687
3.
Mendell, Jerry R, Sahenk. Painful sensory neuropathy. The New
England Journal of Medicine. March 2003; 348(13): 1243-1255
4.
M.G. Serpell, Neuropathic Pain Study Group: Gabapentin in neuropathic syndromes: a randomized, double-blind, placebocontrolled trial. Pain 2002; 99: 557-566

5.
Robert H. Dworkin, Miroslav Backonja, Michael C. Rowbotham.
Advances in Neuropathic Pain. Diagnosis, mechanisms, and treatment recommendations. Arch Neurol. 2003; 60: 1524-1534