Capsaicin, Corticosteroids, and CCK Antagonists

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Capsaicin, Corticosteroids, and CCK Antagonists
Sarah Andreae-Jones MB BS (Smith)
Patron of The Arachnoiditis Trust
England

CAPSAICIN (Zostrix)

Capsaicin is an alkaloid derived from the chilli pepper which has been known in Europe since the time of Columbus in the fifteenth century. 150 years ago, Turnbull([i]) recognised that tincture of capsicum was helpful in treating chilblains and toothache. Capsaicin is the active ingredient in peppers which causes the burning sensation when you eat them.

There is a specific receptor that is activated by capsaicin (termed vanilloid receptor subtype 1 orVR1)which is implicated in both the treatment of chronic pain and urinary incontinence.

Repeated applications deactivate the capsaicin receptor: overstimulating the receptor may destroy the sensory nerve endings.

Repeated administration of Capsaicin is known deplete peripheral neuropeptides, notably Substance P which is known to be essential in pain transmission and is involved in inflammatory conditions such as arthritis. It is therefore most useful for pain of peripheral origin, such as postherpetic neuralgia or diabetic neuropathy.

An easy way to picture this process is to think of what happens when you first eat spicy food: there is a lot of burning in the mouth. However, if you become accustomed to eating curries or chili, you are able to eat food that you would previously found caused intolerable burning.

It is important to note that after a single exposure to capsaicin, the burning occurs rapidly and wears off slowly. Repeated exposure before the burning has dissipated may lead to sensitisation: more intense pain. However, if the exposure is repeated after the burning has stopped, desensitisation occurs: reduction in pain. It seems that capsaicin raises the pain threshold and this can be further raised by gradually increasing the concentration in a series of repeated applications.

Recent literature on treatment of postherpetic neuralgia suggests that capsaicin is a useful part of the clinical armamentarium for this condition. It may also be helpful in orofacial pain, trigeminal neuralgia, atypical facial neuralgia and Burning Mouth Syndrome. Berger et al([ii]) described an extemporaneous formulation of cayenne pepper candy used to treat mouth pain secondary to chemotherapy or radiotherapy; they varied the amount of cayenne pepper, which allowed them to escalate the concentration as the patients’ tolerance developed. Patients who became desensitised to low concentrations tolerated exposure to higher concentrations more easily.

USING CAPSAICIN:

It is available in 0.025-0.075% strength cream/gel OTC. Generally speaking, an adequate trial of capsaicin requires 4 applications a day for 4 weeks. The burning sensation may be relieved by local anaesthetic gel (lidocaine 0.5%) McCleane ([iii]) has tried glyceryl trinitrate (GTN) added to the cream and found that this reduces the burning and may also enhance the analgesic effect.

"Capsaicin usually burns when first applied. It sometimes takes more than a day or two for the effect to kick in, which is when the burning sensation stops. So spending a little more time building up a tolerance to the burning sensation might be one way to make the discomfort a bit more bearable.... It takes something with true detergent action to get this stuff off your skin -- a mild baby shampoo or dish liquid is your best bet -- and a wipe-down with rubbing alcohol won't hurt either. But if you can tolerate it on your skin for at least 15 minutes (so say the package inserts) you will get the benefit even if you have to wash it off later." Source: Anonymous. ([iv])

Adverse effects: as mentioned: burning after each application for up to 5 days after first application.

CAPSAICIN IN COMBINATION:

McCleane has recently published (June 2000[v] ) results of a study of topical application of doxepin hydrochloride, capsaicin and a combination of both and found that they produce analgesia in chronic neuropathic pain. He used 3.3% doxepin hydrochloride, 0.025% capsaicin and a combination of 3. 3% doxepin and 0.025% capsaicin. The results showed “Overall pain was significantly reduced by doxepin, capsaicin and doxepin/capsaicin to a similar extent. The analgesia with doxepin/capsaicin was of more rapid onset. Capsaicin significantly reduced sensitivity and shooting pain. Burning pain was increased by doxepin and by capsaicin and to a lesser extent by doxepin/capsaicin.”

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