Analgesic effects of topical ketamine.

Topical analgesics may play an important role in the management of chronic pain and have good tolerability. Systemic ketamine has limited usage as an anesthetic and along with its potential for addiction and dependence has not gained popularity as an analgesic compound. Topical ketamine however, is devoid of serious side effects, and thus can be used in the management of various pain states such as neuropathic pain and complex regional pain syndrome. Despite using high concentrations of topical ketamine, clinically significant side effects are rare. The measured plasma levels of ketamine and norketamine in various studies were mostly below the threshold of detection. Topical ketamine has been used as compounded formulations alone in concentrations from 0.5% to 20% or in combination with other (co-)analgesics. Its efficacy may depend on the choice of vehicle, the concentration and the pain state. Suboptimal concentration of ketamine and suboptimal pharmaceutical properties of the cream base might have contributed to the negative results of some studies. In this article we will review clinical studies involving the use of topical ketamine for pain.