Neuropathic pain (NP) is a subtype of chronic pain syndrome defined by International Association of the Study of Pain (IASP) as a “pain caused by a lesion or disease of the somatosensory system.” Consequence of CNS or PNS lesions are activities generated in the somatosensory system without peripheral afferent stimulation. The pathophysiology of the somatosensory system is injury causing complex ectopic signaling between neuronal pathways. There are several types of antineuropathic medications that are currently utilized to treat this subtype of pain, including gabapentin, pregabalin, and duloxetine, amongst others.

Oral medication has been the mainstay of therapy; however, the use of topical formulation for chronic pain can reduce serious systemic side effects caused by oral medications. Topical administration of medication via patches, gels, creams, ointments, and solutions can provide local anesthesia and bypass major organ system. Lidocaine is an amide-type local anesthetic agent stabilizing the neuronal membranes by inhibiting the ionic fluxes required for initiation and conduction of impulses. Capsaicin is a selective agonist for TRPV1 receptor expressed in afferent neuronal C fibers and Ad fibers resulting in loss of receptor functionality causing impaired local nociception.Diclofenac works via inhibition of prostaglandin synthesis by blocking COX-1 and COX-2.

The use of cannabinoids and its derivatives for chronic pain is increasing. Two most well-known and clinically relevant forms of cannabinoids are delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD). The main receptor targeted are cannabinoid receptor 1 (CB1) and CB2. Indications for the utilization of THC are multiple sclerosis, cancer-related pain/cancer-related nausea and vomiting (anti-emetic), peripheral neuropathic pain, and HIV-associated weight loss.