|Although post-herpetic neuralgia is generally a self-limiting condition, it can last indefinitely. Treatment is directed at pain control while waiting for the condition to resolve. Pain therapy may include multiple interventions, such as topical medications, simple analgesics, tricyclic antidepressants, anticonvulsants and a number of non-medical modalities. Occasionally, opioids may be required.
Capsaicin, an extract from hot chilli peppers, has been shown to be more efficacious than placebo but not necessarily more so than other conventional treatments.
Substance P, a neuropeptide released from pain fibres in response to trauma, is also released when capsaicin is applied to the skin, producing a burning sensation. Analgesia occurs when substance P is depleted from the nerve fibres. To achieve this response, capsaicin cream must be applied to the affected area three to five times daily.
Patches containing lidocaine have also been used to treat post-herpetic neuralgia. Although lidocaine is efficacious in relieving pain, the effect is temporary, lasting only 4 to 12 hours with each application.
Simple analgesics such as paracetamol and non-steroidal anti-inflammatory drugs have not been shown to be highly effective in the treatment of post-herpetic neuralgia. However, these agents are often useful for potentiating the pain-relieving effects of opioids in patients with severe pain.
Tricyclic antidepressants Tricyclic antidepressants can be effective adjuncts in reducing the neuropathic pain of post-herpetic neuralgia. Tricyclic antidepressants commonly used in the treatment of post-herpetic neuralgia include amitriptyline, nortriptyline, imipramine and desipramine.
These drugs are best tolerated when they are started at a low dosage and given nocte. The dosage is increased every 2-4 weeks to achieve an effective dose. The tricyclic antidepressants share common side-effects, such as sedation, dry mouth, postural hypotension, blurred vision and urinary retention. Nortriptyline and amitriptyline appear to have equal efficacy; however, nortriptyline tends to produce fewer anticholinergic effects and is therefore better tolerated. Treatment with tricyclic antidepressants can occasionally lead to cardiac conduction abnormalities or liver toxicity. The potential for these problems should be considered in elderly patients and patients with cardiac or liver disease.
Because tricyclic antidepressants do not act quickly, a clinical trial of at least 3 months is required to judge a patient's response. The onset of pain relief using tricyclic antidepressants may be enhanced by beginning treatment early in the course of herpes zoster infection in conjunction with antiviral medications.
Phenytoin, carbamazepine and gabapentin are often used to control neuropathic pain. Gabapentin has been shown to be effective in treating the pain of post-herpetic neuralgia, as well as the often associated sleep disturbance.
The anticonvulsants appear to be equally effective, and drug selection often involves trial and error. Lack of response to one of these medications does not necessarily portend a poor response to another. The dosages required for analgesia are often lower than those used in the treatment of epilepsy.
Anticonvulsants are associated with a variety of side-effects, including sedation, memory disturbances, electrolyte abnormalities, liver toxicity and thrombocytopenia. Side-effects may be reduced or eliminated by initiating treatment in a low dosage, which can then be slowly titrated upward.
Effective treatment of post-herpetic neuralgia often requires multiple treatment approaches. In addition to medications, other therapeutic options include transcutaneous electric nerve stimulation (TENS), biofeedback and nerve blocks.
A recent study demonstrated that if famciclovior is administered within 72 hours of the onset of the vesicles of shingles, then damage to peripheral nerves can be minimised and, therefore, the subsequent pain of post-herpetic neuralgia attenuated. The dose of famciclovior is 500 mg orally, three times a day for 7 days.