The September 1, 2014 issue of The Medical Letter includes an article on Drugs for Osteoarthritis, which briefly mentions local application of the nonsteroidal anti-inflammatory drug (NSAID) diclofenac as an alternative to oral NSAIDs. We devoted an entire article to the 1% topical gel formulation of diclofenac (Voltaren Gel) in 2008 when it was first approved by the FDA. We concluded then that it might be modestly effective in decreasing pain in patients with osteoarthritis of the hand or knee with a low risk of systemic NSAID toxicity. We added that how the topical drug compared in efficacy to treatment with an oral NSAID remained to be determined.
The idea of NSAID efficacy without NSAID GI, renal, or cardiovascular toxicity is certainly appealing. Three topical formulations of diclofenac are available now in the US for treatment of various types of pain. In addition to Voltaren 1% Gel, we have a 1.5% topical solution containing dimethyl sulfoxide (DMSO) as a penetration enhancer (Pennsaid), and a diclofenac epolamine 1.3% patch (Flector). According to various reviews, including a 2012 Cochrane review, the question of efficacy relative to oral NSAIDs has been answered positively: topical and oral are equal. Looking at the studies, I am not entirely convinced, but clearly the topical drugs can be effective.
That leaves us with the question of safety and on that both the clinical studies and especially the pharmacokinetics of diclofenac gel are reassuring. Topical diclofenac is absorbed systemically, but the peak serum concentrations are 2% or less of those achieved with oral doses, and the AUC with diclofenac gel is only about 6-20% (depending on the dose) of that with oral diclofenac. As you would expect from those numbers, neither renal nor cardiovascular toxicity has been documented with the topical drug. Some patients have reported GI discomfort, but serious GI toxicity apparently has not occurred.
Our 2008 assessment still seems to be about right: modest effectiveness and low risk. Our September 1 issue will consider the alternatives.
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Diclofenac Gel has been sold over the counter in Europe and in Bermuda, where I practiced Pharmacy, for many years. It helped people with neck and muscle pain but was not effective usually for knees. Since it is so much safer than the oral products its worth a try with patients who have mild or moderate pain in my opinion.
safety ?ODG According to FDA MedWatch, postmarketing surveillance of topical diclofenac has reported cases of severe hepatic reactions, including liver necrosis, jaundice, fulminant hepatitis with and without jaundice, and liver failure. Some of these reported cases resulted in fatalities or liver transplantation. If using diclofenac then consider discontinuing as it should only be used for the shortest duration possible in the lowest effective dose due to reported serious adverse events. Post marketing surveillance has revealed that treatment with all oral and topical diclofenac products may increase liver dysfunction, and use has resulted in liver failure and death. Physicians should measure transaminases periodically in patients receiving long-term therapy with diclofenac. (FDA, 2011) In 2009 the FDA issued warnings about the potential for elevation in liver function tests during treatment with all products containing diclofenac sodium. (FDA, 2009) With the lack of data to support superiority of diclofenac over other NSAIDs and the possible increased hepatic and cardiovascular risk associated with its use, alternative analgesics and/or nonpharmacological therapy should be considered. The AGS updated Beers criteria for inappropriate medication use includes diclofenac. (AGS, 2012) Diclofenac is associated with a significantly increased risk of cardiovascular complications and should be removed from essential-medicines lists, according to a new review. The increased risk with diclofenac was similar to Vioxx, a drug withdrawn from worldwide markets because of cardiovascular toxicity. Rofecoxib, etoricoxib, and diclofenac were the three agents that were consistently associated with a significantly increased risk when compared with nonuse. With diclofenac even in small doses it increases the risk of cardiovascular events. They recommended naproxen as the NSAID of choice. (McGettigan, 2013