TABLE 9.

Anticonvulsants with documented analgesic effects

Agent	Dose range (mg/day)	Mechanism of action	Indications supported by at least one RCT*	Side effects	Comments
Gabapentin (Neurontin†)	1200–3600	N-type calcium channel blocker	PHN, DN, mixed neuropathic pain	Sedation, dizziness ataxia, confusion	Does not require metabolism in liver, so is a better choice in liver dysfunction; clearance will be diminished in renal dysfunction
Pregabalin (Lyrica†)	150–600	α2-δ protein of voltage- gated calcium channels	PHN, DN	Dizziness, somnolence	Analgesic effect is seen within first three days; does not require liver metabolism; renal excretion primary route of elimination
Carbamazepine (Tegretol‡)	200–2000§	Sodium channel blockade	TN	Sedation, dizziness, ataxia, diplopia, hepatitis, rash, hyponatremia	CBC, electrolyte and liver function studies pretreatment and every two weeks for three months, then less frequently§ (the hyponatremia may result in a confusional state); most serious potential side effects are aplastic anemia, hepatitis, serious dermatological reactions¶
Lamotrigine (Lamictal**)	200–400	Sodum channel blockade	TN, DN, poststroke pain, spinal cord injury	Mild rash to serious dermatological reactions††	CBC and liver function studies pretreatment and at four weeks
Oxcarbazepine (Trileptal‡)	600–1200	Sodium channel blockade	TN	Sedation, headache, dizziness, rash¶, vertigo, ataxia, nausea, diplopia, hyponatremia	CBC, electrolyte and liver function studies pretreatment and at four weeks Serious dermatological reactions and multiorgan hypersensitivity reactions have been reported
Topiramate (Topamax‡‡)	50–200	Sodium channel blockade, ↑ GABA inhibition, ↓ glutamate excitation, modulates calcium channels	Migraine prophylaxis	Paresthesia, fatigue, nausea, anorexia, weight loss, changes in taste	Effect is modest; topiramate was associated with approximately one less migraine per month than placebo in three large RCTs

Data from references 115, 117 and 282.

^*For details see section relating to the specific agent in the text;

^†Pfizer Canada Inc;

^‡Novartis Pharmaceuticals Canada Inc;

^§Doses of up to 2000 mg/day may be required in trigeminal neuralgia (TN) (116);

^¶Life threatening dermatological reactions such as Stevens-Johnson syndrome, toxic epidermal necrolysis and lupus may be serious and require discontinuation of carbamazepine and oxcarbazepine;

^**GlaxoSmithKline Inc, Canada;

^††Rash ranging from simple morbilliform type to potentially serious rashes, including Stevens-Johnson syndrome and toxic epidermal necrolysis have been reported (283);

^‡‡Janssen-Ortho Inc, Canada. CBC Complete blood count; DN Diabetic neuropathy; GABA Gamma-aminobutyric acid; PHN Postherpetic neuralgia; RCT Randomized, placebo-controlled trial; ↑ Increases; ↓ Decreases