February, 2016: Do topical NSAIDs penetrate the skin and relieve the pain of osteoarthritis?
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Studies show that topically applied NSAIDs …
Rannou et al: Efficacy and safety of topical NSAIDs in the management of osteoarthritis: Evidence from real-life setting trials and surveys. Semin Arthritis Rheum. 2015 Dec 2. [Epub ahead of print]
Investigators in Montreal recently reviewed all of the randomized controlled trials and meta-analyses related to the efficacy of topical nonsteroidal anti-inflammatory drugs (NSAIDs) for pain relief from osteoarthritis (OA). Most of the studies have been performed on knees, some on hands.
Head-to-head trials of oral vs topical treatment for localized OA showed equal efficacy with lower risk of gastrointestinal averse events (AEs) and higher risk of skin AEs with topical treatment. Topical vs placebo trials showed overall a superior effect of topical NSAID.
Topical diclofenac (Voltaren in the United States) has been the most commonly studied NSAID. One randomized, double-blinded, placebo controlled trial for OA of the hand showed a 42-45% reduction in pain intensity after 4-6 weeks of treatment.
How can this be? The stratum corneum, the outermost layer of skin has a high lipid content and a very low water content and forms a waterproof barrier. Different substances permeate the skin with great variability. Ones that make it through most efficiently have predominantly lipophilic properties but with some hydrophilia. Among all NSAIDs, 20% of etofenamate (not available in the US) is absorbed through the skin. Six percent of diclofenac (Voltaren in the US) is absorbed by this route.
Studies show that topically applied NSAIDs are present in target tissues (fascia, muscles, periosteum) in much greater concentrations than in plasma, at least for knees. These studies were ingeniously performed by having patients who were scheduled for total knee replacement apply the gel regularly for several days before surgery. Then the surgeon biopsied various local tissues and compared the concentration of NSAID compared to plasma.
The authors conclude that because topical administration is safer than oral administration due to lower plasma concentrations and the resultant lower incidence of cardiovascular, intestinal and renal side effects ad that multiple studies show equal effectiveness between the two delivery methods, that topical is preferred, especially in older patients and those unable to tolerate oral NSAID administration.
COMMENT: This article has persuaded me to try it on patients with painful osteoarthritic finger and trapeziometacarpophalangeal joints, especially if they have not obtained satisfactory comfort from heat and rest. I will be looking especially for a patient whose thumb bases hurt equally and ask them to apply it to one side only.