RUBBING IT IN
Applying medicine right to where it hurts certainly has a lot of intuitive appeal. And for people whose gastrointestinal tracts don’t react well to NSAIDs (a common problem), or who are reluctant to take pills for whatever reason, the topical approach is tempting. Here’s a quick rundown of some of the active ingredients in commonly available topical pain relievers.
What is it? Pain relievers in the form of gels and ointments. How does it work? NSAIDs give therapeutic levels of the active ingredient (mostly diclofenac; also ibuprofen, piroxicam, nimisulide in the affected muscles/synovial fluid.) What about side effects? The gastrointestinal problems (stomach upset, ulcers, bleeding) caused by oral NSAIDs are the result of both direct irritation of the gut’s mucosal lining. From what has been seen so far, gels and ointments result in lower NSAID blood levels than the pill forms of the drugs, which translates into fewer side effects, aside from local skin irritation. Does it work? There are doubts. However studies suggest Diclofenac gel might be modestly effective.
What is it? A wintergreen-scented compound that’s an active ingredient in many over-the-counter painrelief ointments. Trolamine salicylate is another salicylate used in topical pain-relief medications. How does it help? When a salicylate compound is absorbed and metabolized into salicylic acid, it has some effect on pain and inflammation, and studies have found that methyl salicylate is well absorbed. A recent study came to the conclusion that aspirin (acetyl salicylic acid) taken orally and a strong methyl salicylate cream were both effective in making blood platelets less “sticky.” Does it work? Products that contain methyl salicylate might provide some pain relief. Trolamine salicylate hasn’t fared so well in studies. Anyone with an aspirin allergy or who is taking blood thinners for cardiovascular disease should consult a doctor before regularly using topical medications that contain salicylates.
What is it? A chemical found in chillies that gives them their hot, spicy taste. Capsaicin is also the active ingredient in several over-the-counter pain products. How does it help? The burning sensation from capsaicin is supposed to do more than just get your mind off the pain, although it does that quite well. In theory, neurons shut down after they’ve been stimulated by the chemical, so the burning and other unrelated sensations – including pain – cease. Does it work? Capsaicin is poorly absorbed, so the low concentrations in OTC products don’t deliver enough of the chemical to neurons to dependably produce the desensitization that is supposed to make capsaicin more than a distracting irritant. Another problem is that people are bothered by the burning sensation, so they don’t stick with the treatment. High-dose capsaicin patches have been developed, but they require local or regional anesthesia and therefore would only be appropriate for treatment for severe chronic pain.
How it helps Menthol’s familiar cooling sensation is the flip side to capsaicin’s burning, although it’s not expected to “max out” neurons and cause desensitization like capsaicin. Essentially, it’s a harmless substance that creates a pleasant diversion from pain or other irritations -- a reasonable goal, particularly if it can outlast the pain, but not really a treatment for the underlying cause of the pain or inflammation. Camphor has a similar effect. Does it work? Like capsaicin, menthol doesn’t change the skin’s temperature; it creates a cooling sensation by attaching to a certain neuronal receptor. Scientists have found that receptor in cancers, so there’s some hope that menthol could be used to make cancer treatment more effective. File this, though, under very preliminary.