COMMENTARY

Topicals in Pain Management: A Review

Charles E. Argoff, MD

Disclosures

November 17, 2011

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Hi. My name is Dr. Charles Argoff, Professor of Neurology at Albany Medical College and Director of the Comprehensive Pain Center at Albany Medical Center in Albany, New York. Today I would like to speak about some interesting data that were presented at the American Academy of Pain Management in September of 2011 in Las Vegas. I would like to talk about the role of topical medications available to us today in the management of acute and chronic pain conditions.

The poster and data that were presented at the American Academy of Pain Management looked at the use of Voltaren® 1% gel (diclofenac sodium topical gel) in the management of osteoarthritis, especially of the knee. It showed a favorable outcome in treated individuals, and also demonstrated a favorable side-effect profile. It actually made me interested in discussing with you the role of topical agents in general.

Importantly, oral agents need to achieve systemic circulation to work. Transdermal agents, such as the fentanyl patch and other agents, use the skin as a route to the systemic circulation. Topical agents -- and this is key because I have seen these terms used incorrectly many times -- work locally. Therefore, one would expect, if you are using a true topical agent, that the concentration of the agent will be localized, with a very reduced and minimal concentration in the systemic circulation. That's important because if you can achieve a balance of benefit by using a topical approach and minimize the side effects that might be associated with the systemic circulation of a particular agent then that is a good balance.

Three topical agents are currently available for the treatment of pain that are considered topical nonsteroidal anti-inflammatory drugs. Five true topical agents in general -- I'll come back to the other 2 in just a second -- are currently available for pain treatment in the United States. The 3 anti-inflammatory medications are all diclofenac-based.

Voltaren 1% gel is approved for the treatment of osteoarthritis of the hands or knees, and/or any areas to which you can actually apply the gel. This is the preparation that was used in the American Academy of Pain Management poster. The other diclofenac approach that is US Food and Drug Administration (FDA)-approved for osteoarthritis (although the approval is limited to osteoarthritis of the knees because that is what was studied) is a medicine called Pennsaid (diclofenac sodium topical solution). That stands for "penetrating nonsteroidal anti-inflammatory drug." This is also diclofenac based, but it's diclofenac in dimethyl sulfoxide solvent. It is believed that the solvent helps to better penetrate the joint. It is interesting that although the Voltaren 1% gel studies have not compared the gel with oral agents, Pennsaid, in at least one study, was compared with oral diclofenac, which we commonly use as well. This study found essentially equal benefit, but a much more favorable side-effect profile with Pennsaid. That is important information because that is the kind of balance we want to achieve.

For acute pain (acute sprain and strain-type injuries) we have the Flector Patch (diclofenac epolamine topical patch). It's a topical system that looks very similar to the lidocaine patch and can be used for acute muscle sprain and strain-type injuries.

Moving on to the other agents, the lidocaine patch (Lidoderm®) is a 5% lidocaine system. Patients can use up to 3 patches for 12 hours each. This is the official recommendation, although many people use up to 4 patches per 24 hours based upon studies that have been done, but that's not the way it was approved by the FDA. The only indication for the lidocaine patch is for postherpetic neuralgia. However, there have been many reports of its use in other neuropathic pain states, including diabetic peripheral neuropathy, complex regional pain syndrome, and chronic musculoskeletal pain.

Finally, the newest agent to be available from a topical point of view is the Qutenza® patch. This is an 8% capsaicin patch that needs to be applied in a very specific way. Many of you are familiar with capsaicin as the extract from chili peppers. Capsaicin specifically addresses activity at the TRPV1 receptor (a sensory receptor) in the skin. Capsaicin helps to turn it off and functionally deactivate it for up to 12 weeks when the patch is used. This is a very important receptor for the initiation of pain. It has been shown to be effective in postherpetic neuralgia, as well as other conditions. In fact, it is FDA-approved for postherpetic neuralgia as well.

When treating someone with the Qutenza patch, it needs to be done in an office setting. Before the patch is applied, there is a pre-application of topical lidocaine or prilocaine combination cream for an hour over the area where the patch is going to be applied. Then you have to very carefully trace out the area to which you want to apply the patch, place the patch and overlap that carefully traced-out area, being very careful to not aerosolize the capsaicin because it could be very toxic to you, as well as the person who is receiving the patch. Leave the patch on for an hour, followed by an hour observation period.

The beauty of the topical approach is that they have limited drug-drug interactions and systemic side-effect potential. With the Qutenza patch, the only side effect other than pain associated with burning of the capsaicin is a slight elevation of blood pressure in some individuals.

We now have 5 agents that would be considered topical agents. Some of the agents have been shown to be at least equal in benefit to an oral agent of the same type. They can be used in association with other treatments, but the idea in using the topical agents from a clinical point of view is to try to get the same or a similar clinical benefit without the side effects of the oral agent.

One last point, for those of you who say, "How could it work if it's in the skin?" Work being done around the world -- not just in the United States and Europe -- has demonstrated the importance of the skin as a major organ in the initiation, maintenance, and modulation of pain. It may be that the skin is far more important than we ever thought in helping people control their pain. Thank you.

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