Efficacy and Safety of Topical Analgesics for Osteoarthritis of the Knee
Non-steroidal anti-inflammatory drugs, or NSAIDs, are used to alleviate pain and inflammation associated with many conditions, including a type of arthritis called ]]>osteoarthritis]]> . Osteoarthritis is characterized by a degeneration of the cartilage in the joints. Once the cartilage has worn away, the bones in the joint rub against each other causing pain and inflammation. This type of arthritis can involve any joint, but the knees and hips are most often affected. Although it is not an inevitable part of aging, increasing age is risk factor for developing osteoarthritis.
Unfortunately, while oral NSAIDs are effective at relieving the pain of osteoarthritis, they carry the potential for significant adverse reactions that can affect the gastrointestinal tract, liver, and kidneys. The risk of these side effects rises in elderly patients, the same population that is more likely to have osteoarthritis.
One way to reduce these adverse effects is to keep as much of the medication as possible out of the blood stream by delivering it topically rather than orally. In the past, however, topically administered pain medications did little to relieve the pain of osteoarthritis. But a new study published in the October 11, 2004 issue of the Archives of Internal Medicine investigated the effectiveness and safety of a new topical NSAID for relieving the symptoms of osteoarthritis in the knee. The authors concluded that overall, the topical NSAID was more effective than a placebo.
About the Study
This study randomly assigned 326 patients diagnosed with osteoarthritis of the knee to receive either 40 drops of a topical NSAID (called diclofenac 1.5%) four times daily or a placebo. The study lasted 12 weeks, and patients were evaluated on three outcomes:
- Physical functioning
- Global assessment (overall well being)
Stiffness and “pain on walking” were also evaluated for each patient. The study medication, diclofenac, is an NSAID prepared in a topical solution that allows it to be absorbed through the skin. The drug was applied to the afflicted knee, with 10 drops applied to each surface of the knee (front, back, and both sides).
The results of the study revealed the topical NSAID was significantly more effective at reducing pain, physical functioning, and global assessments than the placebo. The most common adverse event in the group receiving the active drug was minor skin irritation, which occurred in 68 out of 164 patients. The study did not find any significant differences between the groups in terms of gastrointestinal irritation or other adverse effects.
The authors concluded that topical diclofenac is effective at relieving the symptoms of osteoarthritis, including pain. The main adverse effect was local irritation, and no other significant adverse events were seen.
How Does This Affect You?
As our age increases, so do our health risks. In addition to a higher risk of developing disorders like osteoarthritis, older adults may be at a higher risk for adverse drug effects. Older adults may require higher doses to treat more advanced conditions and are more likely to be taking multiple medications that can adversely interact with one another. Furthermore, medications are not cleared from the bloodstream as efficiently as they used to be, which may lead to a gradual build up of drugs in the body.
Despite these hazards, the pain of osteoarthritis cannot remain untreated. Fortunately, if drugs like the one used in the study become available, doctors and patients will have another option for pain relief. The results of this study suggest that a topical therapy may be able to provide pain relief without the associated risks posed by orally administered medications. In fact, the American College of Rheumatology has recommended topical therapy for those patients who cannot tolerate oral or systemic NSAIDs. Also, Vioxx®, a newer type of NSAID (called a COX-2 inhibitor) was recently taken off the market due to potentially life-threatening side effects. This may further open the market for effective topical therapies. The drug used in the study (Pennsaid®) is approved for use in Canada and some European countries, but it is still under investigation by the Food and Drug Administration in the US.
While these results are encouraging, the researchers did not address the question of which is more effective, topical or oral NSAIDs. If oral NSAIDs turn out to work significantly better, patients may be willing to tolerate their higher risk of adverse effects. Now that we know that at least one topical NSAID appears to be effective for osteoarthritis of the knee, the next step would be test it against a popular oral agent for both effectiveness and side effects.
The Arthritis Foundation
Information on Legislation and prescription drugs from the AARP
Lin J, Zhang W, Jones A, Doherty M. Efficacy of topical non-steroidal anti-inflammatory drugs in the treatment of osteoarthritis: A meta-analysis of randomized controlled trials. 2004. BMJ. Available at: http://bmj.bmjjournals.com/cgi/reprint/bmj.38159.639028.7Cv1 . Accessed October 12, 2004.
Managing osteoarthritis: Helping the elderly maintain function and mobility. Available at: www.ahrq.gov. Accessed October 12, 2004.
Osteoarthritis. 2004. available at: http://www.arthritis.org/conditions/DiseaseCenter/oa.asp . Accessed October 12, 2004.
Risk of NSAID-induced toxicity in older adults. Available at: www.aafp.org/ afp/970901ap/tips6.html. Accessed October 12, 2004.
Roth SH and Shainhouse JZ. Efficacy and safety of a topical diclofenac solution (Pennsaid) in the treatment of primary osteoarthritis. Arch Intern Med. 2004. 164: 2017-2023.
Last reviewed Oct 14, 2004 by ]]>Richard Glickman-Simon, MD]]>
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