Topical analgesics

Among the drugs with well-known peripheral effects are nonsteroidal anti-inflammatory drugs (NSAIDs), local anesthetics, and capsaicin. Less well appreciated is the fact that nitrates, tricyclic antidepressants (TCAs), glutamate receptor antagonists, alpha-adrenoerecptor antagonists, and cannabinoids may have an analgesic effect when applied topically. The rational for the analgesic effects of these compounds, when applied topically, is discussed in this article. To patients, it makes sense to apply pain relief directly to where they feel pain. They know that oral medication can produce side effects, whereas topical agents are less likely to do so. Knowledgeable physicians, however, understand that pain is influenced by peripheral and central factors. They understand that significant opportunity exists to augment inhibitory or to lessen facilitatory influences on the pain stimulus, and therefore, in general, seem to prefer systemically active agents. Increasing evidence, however, backed up by clinical use, now suggests that topically applied medication can be at least as effective as that administered by the oral route and, in general, has a more favorable side effect profile than orally active agents. In this article, the author looks at medications that have a tradition of topical use and at newer additions to this range of drugs. Although a rich variety of potential pharmacologic targets exists peripherally, to date, only some of these are amenable to currently available therapeutic entities; it is on these that concentration is focused. Not all medication applied to the skin has a local, peripheral action. Drugs such as fentanyl and buprenorphine, which can be applied to the skin, have predominately central effects. This type of administration is known as transdermal to distinguish it from the topical analgesics-drugs that are applied to skin and have a predominate peripheral effect.