Discussion: Analgesic Options
SSRI antidepressants. Although antidepressants can be effective for neuropathic pain, the SSRI antidepressants have been found to be less effective than the tricyclic antidepressants (TCAs), such as nortriptyline and desipramine, and the serotonin-norepinephrine reuptake inhibitors (SNRIs), such as duloxetine and venlafaxine. The reason for this difference is the underlying mechanism of action of these drugs. Antidepressants are thought to produce activity in the endogenous modulating pathways that originate in the brainstem and descend to the spinal cord, where amines, such as serotonin and norepinephrine, are released. By blocking the body's reuptake (resorption) of these neuroinhibitors, antidepressants presumably increase activity in these modulatory pathways.
Although low serotonin levels have been shown to be powerful mediators of depression, serotonin plays a lesser role than norepinephrine in producing analgesia. This helps to explain why the SSRIs are effective in relieving depression but not particularly effective in relieving pain, and why the antidepressants with more norepinephrine-selective activity, such as the TCAs and SNRIs, are recommended as first-line analgesics for the treatment of neuropathic pain syndromes, such as postherpetic neuralgia.[1,3,4] The anticonvulsants gabapentin and pregabalin are other first-line options.
Lidocaine patch 5%. The topical lidocaine patch 5% is US Food and Drug Administration-approved and is considered a first-line analgesic agent for the treatment of postherpetic neuralgia.[3,4] The 10 cm x 14 cm patch contains 700 mg of lidocaine. It is placed directly over the painful area and may be cut to fit smaller areas. The manufacturer states that up to 3 patches can be applied simultaneously to intact skin for up to 12 hours in any 24-hour period. However, research has shown that wearing 4 patches continuously for 24 hours, and then replacing them with new patches, is also safe. The drug is well tolerated by most individuals, and the most common side effect is a transient dermal reaction.
The lidocaine patch 5% can be used alone or with a systemic drug regimen, such as an antidepressant or anticonvulsant, to provide additive relief if necessary. A potential benefit of the lidocaine patch for the patient in this scenario is a reduction of allodynia, a common feature of neuropathic pain in which a nonnoxious stimulus (eg, wearing clothing) produces pain. The patch should be applied only after the vesicles of acute herpes zoster have healed, to prevent increased systemic lidocaine absorption and a very painful patch-removal experience.
Opioid analgesics. Opioid analgesics, such as morphine and oxycodone, are effective for all types of pain but are considered second-line treatment for neuropathic pain.[3,4] An opioid may be added to improve efficacy, particularly if the pain continues to be moderate to severe despite first-line treatment and has a significant effect on the patient's quality of life. Because the pain of postherpetic neuralgia is typically continuous in nature, a long-acting opioid (such as sustained-release morphine or controlled-release oxycodone) is indicated.
NSAIDs. NSAIDs are effective for nociceptive, inflammatory types of pain, such as pain following surgery or trauma, but they are among the least effective agents for relief of neuropathic pain. NSAIDs can be helpful in reducing the pain associated with acute herpes zoster but are unlikely to relieve the persistent neuropathic pain of postherpetic neuralgia and are not listed as options in neuropathic pain treatment guidelines.
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Cite this: Chris Pasero. The Burning, Searing Pain of Postherpetic Neuralgia - Medscape - Dec 19, 2012.