There are topical anti-inflamatory preparations where the advertising at least implies that they work topically, in that the effect will be more localised by the use of a topical preparation than if the same medication was taken systemically, such as in pill form:
Nurofen Max Strength Joint & Back 10% Gel contains ibuprofen known for its anti-inflammatory properties and is absorbed into the skin to get to work where its needed. Whether its lower back pain, joint pains or a strained calf muscle, with Nurofen Gel you can rub in pain relief directly where it hurts.
Without knowing anything specific about this, I doubt this claim. Diffusion is slow, for example August Krogh reports that diffusion of gasses through animal tissue is much slower than through water or gelatine, and a value of 0.115 cubic centimetre of oxygen per minute penetrating 0.001mm of connective tissue is given. The circulatory system is very efficient, supplying all tissues with oxygen and removing all waste products. It seems at least plausible that the effect of topical anti-inflamatory gels may actually work via the general circulation, ie. more is absorbed by the blood in the skin and transported to the site of action by the circulatory system than diffuses directly from the site of application to the site of action.
Is there any work that attempts to quantify these effects? An obvious way would be to apply the gel to one knee and measure the concentration of the active ingredient in both joint capsules, but there may be a less destructive way of doing it.
