1. Up to 40% of patients with neuropathic pain may be refractory to drug treatment. It is important to avoid the development of secondary ‘chronic pain disorder’ by maintaining emotional and physical ‘fitness’, physiotherapy (especially in complex regional pain syndrome), TENS, and referral for multidisciplinary pain management if distressing symptoms persist.
2. Theoretically in neuropathic pain prescribing should be based on the patient’s symptoms and signs ie mechanisms of pain rather than pathophysiological diagnosis. In practice, tricyclic antidepressants and antiepileptics remain the most useful drugs. Some topical agents can be helpful eg capsaicin cream.
3. Like any analgesic these adjuvant drugs have a ceiling effect for pain relief and side effects. Unlike conventional analgesics their side effects are often noticed by the patient before the ceiling effect for pain relief is reached. Therefore the drugs should be given slowly and titrated upwards over a period of time with careful monitoring of side effects. When used for chronic pain it is advisable to review their effectiveness every three months.
4. The drugs are listed below taking their side effects into account. Titration times are suggested below for guidance if a practitioner is unfamiliar with using these classes of drug as adjuvant analgesics.
5. Tricyclic antidepressants eg amitriptyline are generally first line treatment (although unlicensed for this indication). Start with 10 mg at night for 1 week (a starting dose of 5 mg in the very elderly). Then increase by 10 mg weekly until effective or side effects occur. Average daily dose in the range 30 - 50 mg, maximum daily dose 75 mg.
6. Gabapentin is generally a second line choice. Start at 300 mg daily and increase by 300 mg a day to 300 mg TDS. If not effective at this dose after 7 - 10 days increase by 300 mg a day to 600 mg TDS. Note that elderly patients may require the lowest possible initial dose or a longer titration period. For instance start at 100 mg nocte and increase by 100 mg a day to 100 mg TDS. If not effective at this dose after 7 - 10 days increase by 100 mg a day to 200 mg TDS. Patient benefit should be gauged from a trial period of about 8 - 12 weeks, using the minimum effective dose. All patients should be reviewed after 6 months. Try slow downward dose titration to see if lower maintenance dose or stopping is possible. Always stop slowly.
7. Carbamazepine: titrate 100 mg TDS to 300 mg TDS over a period of 3 to 6 weeks. Maximum recommended dose 1.2 g daily in divided doses.
8. Sodium valproate: titrate 200 mg BD to 300 mg BD (maximum suggested dose).
9. Mianserin and 5HT drugs have been excluded, as they are ineffective.
10. If spasm present consider diazepam (eg for muscle spasm) or hyoscine butylbromide (eg for renal / bowel spasm).
11. Topical capsaicin 0.025% or 0.075% may have a place for post-herpetic neuralgia but not for shingles. Apply QDS for 6 weeks using 5% lidocaine cream as a pre-treatment if necessary.