Natural Medicines Newsletter

Volume 1, Issue 13, 04/16/2009

Question

Part 1: What is the mechanism by which topical capsaicin initially causes pain (a burning or stinging type of feeling) and possibly mild redness and swelling when being used for chronic pain management?

Answer

This is part 1 of a 2 part series.  Capsaicin is the pungent ingredient found in chili peppers from the genus Capsicum (Solanaceae) and, when eaten, gives the peppers their "hot" taste.(1,2)  As it relates to its use in medicine, capsaicin is most commonly used for the treatment of pain and can be purchased in the form of a topical cream or gels in concentrations ranging from 0.025% to 0.075%.  Common brand names include Arthicare®, Capsagel®, Capzasin-P®, Zostrix® and Zostrix-HP® and can be without a prescription in most countries.  The most common pain syndromes treated with topical capsaicin include rheumatoid arthritis, osteoarthritis and psoriasis.(2-4) Topical capsaicin can be a useful adjunct in pain management, especially when escalating doses or addition of other medications is likely to lead to intolerable systemic side effects or drug interactions.(1-4)  Unfortunately, this treatment is plagued with a slow onset of therapeutic benefit, during which time patients frequently experience feelings of pain or burning, redness, and  possibly minor swelling in the area of application.  Why and how does capsaicin cause this side effect prior to producing noticeable pain relief for the patient?
 
In the skin, there any many free nerve endings that are connected to and activate sensory afferent nerve fibers when stimulated. Sensory afferent nerve fibers carry nerve impulses generated in the peripheral tissue toward the spinal cord, which then communicate with other neurons in the spinal cord to eventually deliver the message of pain for perception and interpretation by the brain.(5)  The nerve impulse or fiber is sensory if it carries pain, temperature, touch, vibration, pressure or proprioceptive information to the brain.(5)  Also, it is important to know that there are different types of pain conducting sensory nerve fibers such as A-alpha, A-beta, A-delta, and C, which are listed from fastest conduction velocity to the slowest.(5)  Therefore, C-nerve fibers are the slowest and can be further differentiated from other nerve fibers as they are also  unmyelinated.(5)  Why is this level of differentiation of sensory nerve fibers so important when considering capsaicin's initial mechanism of action?
 
Other keywords found in this issue: peripheral nerve ending, neuropeptide, substance P, calcitonin gene related peptide (CGRP), vasoactive intestinal peptide (VIP), lateral Spinothalamic tract, spinal lemniscus, cerebral cortex, post central gyrus, Na, Ca, K......To read the full answer please LOGIN or SUBSCRIBE NOW.