A single one-hour localized, office-applied treatment with prescription-strength 8% capsaicin (a synthetic form of the ‘heat’-producing compound found in chili peppers) can provide three months relief from postherpetic neuralgia – (PHN), the ‘nerve pain’ that can follow shingles.
Originally limited to over-the-counter, lower-strength topical applications, capsaicin works by depleting or interfering with substance P, a chemical that transmits pain impulses along nerve pathways to the brain. The drug (Qutenza®) was FDA approved in Nov 2009 for management of neuropathic pain associated with postherpetic neuralgia. Potentially useful for HIV neuropahy and diabetic neuropathy as well based on early testing, the drug is:
• Unlikely to cause drowsiness or interact with other drugs.
• And can be used alone or with other pain medications.
What is Post Herpetic Pain?
Each year, about one million Americans develop shingles, a painful viral infection caused by a reactivation of the same virus that causes chickenpox. It is estimated that up to one in five people with shingles will experience prolonged pain after shingles, known as PHN. The pain can persist long after the shingles rash clears up and can disrupt sleep, mood, work and the activities of daily living.
“PHN can be an excruciatingly painful condition that can greatly affect many aspects of a person’s daily living,” said Lynn Webster, MD, medical director, Lifetree Clinical Research, Salt Lake City, Utah. “Despite the current availability of a variety of pain medications, undesirable side effects, such as drowsiness and interactions with other drugs, often limit their use.
“Because of these limitations, there is still a need for new treatment options for PHN, and, more importantly, many patients are still suffering. Qutenza may provide a unique treatment option for patients. It is targeted directly to the site of the pain and may be used alone or in combination with existing therapies.”
One-Hour Application, Lasting Effect
Qutenza is applied directly to the painful site by a physician, or health care professional under the close supervision of a physician.
• Applied to marked areas on the skin, the treatment is accompanied by a numbing agent applied to these areas, possibly along with cold packs and pain medicine. (The initial effect of application is an intense burning sensation, which later subsides.)
• Up to four patches may be used.
• They may be cut to conform to the size and shape of the painful area.
• Treatment may be repeated every three or more months as warranted by the return of pain,
• But not more frequently than every three months.
In clinical trials, the most common side effects were application-site redness, pain, itching, and papules (small bumps). The majority of these reactions were local, transient and self limited. Among patients treated with Qutenza, 1 percent discontinued prematurely due to an adverse event. Serious adverse reactions included application-site pain and increased blood pressure.
Increases in blood pressure occurred during or shortly after exposure to Qutenza and were associated with treatment-related increases in pain. The changes were on average less than 10 mm Hg, although some patients had greater increases, and these changes lasted for approximately two hours after patch removal.
Educational in-service training will be available online and on DVD for health care professionals interested in prescribing and administering the drug; and patients will be able to locate doctors who may prescribe the drug at Qutenza.com.
Another Capsaicinoid in Trials for Advanced Cancer Pain
Another high strength capsaicin compound (Resiniferatoxin), from the sap of a Moroccan plant is now in NIH-funded human trials as a potential morphine alternative for severe advanced cancer pain. At 1,000 times the potency of capsaicin in chilis, this experimental drug does more than numb neurons in the pain messaging system; it ‘shatters’ and kills them. Injected under general anesthesia in the spinal cord of dogs with bone cancer in earlier animal trials, it enabled the animals to move and play again, apparently pain free, for weeks to months.
Sources: NeurogesX, Inc. news release Apr 6; Southern Illinois University School of Medicine news release, Nov 3, 2009.