Medications in Treatment of Postherpetic Neuralgia

Abstract

Among many various neuropathic pain syndromes, postherpetic neuralgia (PHN) is one of the most typical and difficult neuropathic pains to control in some patients. To prevent progression to PHN, vaccination against herpes zoster has been developed. There are reviews about herpes zoster vaccination in recently published articles in the Korean Journal of Pain (KJP) and other journals [1,2]. As is written in those and other reviews, once herpes zoster progresses to PHN, the syndrome could result in severe personal and social burdens for patients. Although PHN has been known for a long time and is a typical neuropathic pain, many treatment modalities and options continue to be reported. There have even been case reports on the effectiveness of systemic vitamin C administration and transforaminal epidural magnesium injection [3-6]. The treatment for PHN varies among hospitals, and commonly used pharmacological and interventional methods include anticonvulsants and interlaminar epidural blocks [7]. According to the suggested treatment algorithm for acute or subacute herpes zoster and PHN, adjuvant pharmacological medications are tricyclic antidepressants, anticonvulsants, opioids, tramadol, topical lidocaine, and capsaicin [8]. In this month's issue of KJP, Joo et al. [9] report on the controllability of PHN with nefopam. They used systemic nefopam during the titration of the oral medication. Although there have been many clinical reports on nefopam for the treatment of pain, to date, few reports may be found regarding the treatment of chronic neuropathic pain. Nefopam has been known to be effective in acute postoperative pain and postanesthetic shivering [10-13]. In animal research, intrathecal nefopam is reported to have an antinociceptive effect in an acute inflammatory rat pain model [14]. Systemic administration of nefopam was shown to enhance the analgesia with morphine and nimesulide and decrease pain behavior and reduce adverse effects in a chronic constrictive nerve injury rat model [15]. Nefopam's mechanism of action is suggested to be through the activities of the serotonin, glutamate, and dopamine circuits [16], and it might be successfully tried in the treatment of various chronic neuropathic pain conditions. If we consider the chronicity and intractability of many neuropathic pain conditions, and the continuity of medication in these patients, many trials for neuropathic treatments are anticipated.