Topical Analgesics: a Review of Recent Clinical Trials and Their Application to Clinical Practice*

Topical analgesics can play an important role in the therapeutic armamentarium for pain management. The mechanism of action of topical analgesics is largely within the peripheral nervous system. However, recent clinical investigations suggest that the effect of topical analgesics on peripheral processing of pain transmission may lead to the dampening of central pain mechanisms as well. Thus, indirectly, topical analgesics may act to relieve the discomfort associated with central, as well as peripheral, pain states. This article summarizes recent studies of the use of topical analgesics in varied chronic pain conditions. Much of the recent clinical research on topical analgesics has been conducted using the topical lidocaine patch 5%. (Adv Stud Med. 2003;3(7A):S642-S647) D espite ongoing research and therapeutic advances, most physicians who treat pain recognize that significant challenges remain. Regardless of the source or pathophysiology of the individual pain experience, patients often gain only partial relief. Systemic analgesic regimens, such as nonsteroidal antiinflammatory drugs, tricyclic antidepressants, opiates, and alpha-adrenergic receptor antagonists, play a significant role. However, these regimens are often limited by tolerability issues associated with their use. Given these limitations, topical analgesics are being investigated as an additional option in the management of chronic pain. Because topical analgesics exert their pharmacologic activity at the site of pain, they are associated with minimal systemic absorption and provide a targeted means of delivering analgesia, without systemic adverse effects. They can be used regularly and consistently over time with no significant systemic accumulation, minimizing risks of adverse effects and drug-drug interactions more likely to occur with systemic analgesics. This is a distinct advantage, particularly in older patients, who are more likely to be taking systemic medications concomitantly with pain management therapies. In contrast, transdermal systems, such as the fentanyl patch, exert their activity through systemic drug absorption and therefore can be applied at any site on the body to which patches can adhere. The variations between topical and transdermal application systems are summarized in Table 1. The topical lidocaine patch, the first drug approved by the US Food and Drug Administration (FDA) with an indication for postherpetic neuralgia (PHN), provides an effective treatment option with minimal adverse effects. The topical lidocaine patch 5% is a pliable 10 x 14-cm patch that can be affixed directly to the affected areas. Multiple patches may be PROCEEDINGS