Arthritis Information

Understanding Topical Analgesic Therapy for Arthritis Pain
(An excerpt from U.S. Pharmacist)

What is Arthritis?
Managing Arthritis Pain
External Analgesics for Arthritis Pain
When to Use External Analgesic Products
Safety of External Analgesics
Advising Patients on Treating Arthritis Pain with Topical Analgesic Therapy

What is Arthritis?
Arthritis is America's leading crippling disease, affecting some 70 million Americans everyday. More than a million new cases are diagnosed each year. The disease consumes an estimated $82 billion a year in health care costs and lost wages.

While there is no cure for arthritis, there are a number of treatments that can modify the pain and inflammation associated with it. Patients, however, may comply poorly with such treatments because of side effects or because they forgot to take a dose. Patients may turn to topical analgesics as a way to obtain relief with minimal adverse effects. Since these products are available without a prescription, they can be easily obtained. A pharmacist can help them select an appropriate topical product and teach them how to use it.

But before a pharmacist can help a patient, he must first help them understand their disease. Arthritis refers to nearly 100 inflammatory conditions that affect joints and connective tissue, but the two most common forms are osteoarthritis and rheumatoid arthritis.

Also known as wear-and-tear arthritis, osteoarthritis is characterized by deterioration of articular cartilage, bone hypertrophy and changes in the synovial membrane. Incidence of this form of arthritis increases with age with as many as 80 percent experiencing it by age 65.

Rheumatoid arthritis is a chronic inflammatory autoimmune disorder that afflicts an estimated two million Americans at a younger age and occurs more commonly in women. It appears in several joints and often in the hands and feet.
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Managing Arthritis Pain
Management of arthritis pain can be achieved through oral medication, non-pharmacologic approaches and external analgesics. Non-steroidal anti-inflammatory drugs (NSAIDs) are the most frequently prescribed form of therapy. While these drugs are effective analgesics in low-to-moderate doses, they are not suitable for everyone. Between two and four percent of patients taking them experience adverse reactions. Elderly people are at a higher risk as toxicity is increased with other drugs they might be taking.

Therefore, there is a need for safe and effective therapy to manage arthritis pain when systemic (e.g., oral medication) therapy is not suitable or adequate.

Besides using oral NSAIDs for treatment of osteoarthritis, physicians will occasionally prescribe analgesic acetaminophen or intra-articular corticosteriods. In addition to physician prescriptions, patients may self-medicate with over-the-counter (OTC) oral analgesic products. However, adverse effects are common (as with aspirin).

Non-pharmacologic therapy, including rest, heat, cold, physical therapy and alteration of the patients' lifestyle and work activity, may also be suggested, but these measures only help to relieve pain and may only delay further joint damage.
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External Analgesics for Arthritis Pain
In addition to oral analgesics, external analgesics may be applied to the skin to relieve musculoskeletal pain including arthritis. In the tentative final monograph for OTC external analgesics, a panel of experts endorsed a number of active ingredients for use in OTC external analgesics. They classified these into four main groups, as indicated by the following representative compounds:

1. Methyl salicylate, which occurs in wintergreen and sweet birch oil, is one of the more potent counterirritants. The recommended topical dosage is a 10 to 60 percent concentration applied three to four times daily. Methyl salicylate readily penetrates intact skin after application.

Because of the possibility of percutaneous absorption, methyl salicylate should be used with caution in individuals who are sensitive to aspirin or suffer from asthma or nasal polyps. Also, patients should be told not to use heating pads in conjunction with methyl salicylate, or external analgesics in general, or to apply them after strenuous exercise, especially during hot and humid weather. These conditions can magnify the extent of systemic absorption, and in the case of methyl salicylate have resulted in reports of severe adverse reactions.

2. Menthol is a less potent counterirritant than methyl salicylate and produces a cooling sensation in the skin. It is a secondary alcohol extracted from peppermint and can be made synthetically. It can be found in candy, chewing gum, cigarettes and even cough drops. In concentrations from 1.25 to 16 percent, menthol possesses counterirritant properties, in some cases merely replacing one sensation with another. Counterirritant concentrations of menthol applied topically produce a feeling of coolness followed by a feeling of warmth. The sensation of cold is not due to actual cooling of the skin; menthol induces vasodilation (dilation of blood vessels), and the skin temperature at the site is actually warmer than other parts of the body.

Menthol can cause sensitization in some individuals. Adverse reactions include urticaria (hives), erythema (redness), and other cutaneous (skin) reactions.

3. Methyl nicotinate is categorized as a vasodilator. When applied three or four times a day in concentrations of 0.25 to one percent, it is a safe and effective counterirritant. Vasodilation (dilation of blood vessels), erythema (redness) and an increase in skin temperature occur with application. Changing the concentration will not change the rate of absorption, but will increase the intensity of the reaction.

The vasodilatory action of methyl nicotinate can be blocked, at least in part, by prior administration of ibuprofen or other NSAIDs, indicating the methyl nicotinate may induce vasodilation secondary to an increase in prostaglandin synthesis. When methyl nicotinate is applied over large body surface areas, generalized vasodilation can occur, and some individuals have experienced large reductions in blood pressure and syncope (fainting) as a result.

4. Capsaicin is the active ingredient in red chili peppers. It relieves the pain of arthritis and musculoskeletal disorders effectively, as well as pain associated with neuralgias. The same way that biting into a hot chili pepper incites a powerful stimulation of local sensory receptors in the mucous membranes, capsaicin, when applied topically in weak solutions, can cause a sensation of warmth.

In clinical studies, a double-blind, placebo-controlled study of topical capsaicin 0.025 percent (Zostrix®) demonstrated that it significantly relieves pain caused by osteoarthritis and rheumatoid arthritis. Patients with osteoarthritis or rheumatoid arthritis of one or both knee joints were randomized into a double-blind, placebo-controlled multicenter study. Compared to the group that received the placebo, the capsaicin-treated groups experienced a significant reduction in pain after one week. Similar results were noted in another study of patients with osteoarthritis of the hand.

No systemic side effects or drug interactions were reported in either study. Adverse effects, which include burning, stinging and erythema, were localized to the site of application and normally diminished with repeated use. Clinical trials demonstrate that long-term use of capsaicin does not result in tachyphylaxis (decline in efficacy with continued use) or development of adverse effects.

Other common topical ingredients include eucalyptus oil, trolamine salicylate, emu oil, MSM, witch hazel, glucosamine and chondroitin. None of these has shown significant analgesic or anesthetic efficacy when applied topically and they are not approved in the tentative final monograph for OTC external analgesics.
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When to Use External Analgesic Products
Over-the-counter external analgesic products are used for a wide variety of afflictions such as aches and pains associated with musculoskeletal disorders like arthritis. They are appropriate for any patient who needs pain relief and may be used on their own or as an adjunct to systemic therapy.
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Safety of External Analgesics
Absorption of external analgesics through the skin is minimal when the products are used as directed, making them safe. If swallowed, however, some may be extremely toxic and should be kept out of the reach of children. Excessive rubbing or bandaging of the area of application may cause blistering. Persons sensitive to the ingredients may develop a rash that may be difficult to distinguish from erythema. If a rash or irritation appears, the product should be discontinued and the area washed and rinsed thoroughly. Persons sensitive to aspirin may react adversely to methyl salicylate.
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Advising Patients on Treating Arthritis Pain with Topical Analgesic Therapy
Pharmacists play a key role in educating patients on the proper use of external analgesic products. Since external analgesics are available over the counter, patients will most likely consult a pharmacist much more commonly than their physician and statistics show that only 38 percent of Americans obtain information about arthritis from their physicians. The pharmacist, therefore, can be an invaluable resource for patients seeking arthritis relief and can help them get the most from analgesic therapy. Many arthritic patients will be taking systemic medication for analgesic and/or anti-inflammatory action. They should be advised to continue this therapy while initiating treatment of external products. Once they respond to the topical product, they may be able to decrease their dosage of systemic analgesic therapy but should do so only after consulting with their physician.

Pharmacists should not confuse capsicum, capsicum oleoresin, and capsaicin. Products labeled as containing capsicum, capsicum oleoresin or capsaicin oleoresin have not been demonstrated to have equivalent therapeutic action to those containing purified capsaicin. Evidence of clinical safety and a reputable manufacturer that uses good manufacturing practice (GMP) should strongly influence selection and recommendation of products.

Patients using topical capsaicin must take particular care in following directions. Topical capsaicin must be applied three to four times daily for maximum benefit. Relief may be experienced within a few days but it often takes two or more weeks before patients feel maximal relief.

As with all medical treatments, patients should be advised to expect that a particular analgesic may reduce their pain, but rarely will any treatment, topical or otherwise, alleviate all pain associated with arthritis.
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THE ABOVE INFORMATION HAS BEEN EXCERPTED FROM:

Thomas A. Gossel, R.Ph., Ph.D., Understanding Topical Analgesic Therapy for Arthritis Pain, U.S. Pharmacist Supplement, 1994.