In Reply.—
The claims of Nazarro-Porro and coworkers regarding the therapeutic properties and lack of toxicity of azelaic acid bring to mind the home-cleaning salesman who claims that his product not only can clean the oven, sink, floor, finest china, and commode, but also is nontoxic to humans and pets and can be used as fertilizer for plants. A basic premise of modern pharmacologic therapy is that most useful compounds have therapeutic windows below which they are ineffective and above which they are generally toxic. While these investigators appear to have stumbled on (quite literally) a useful compound due to a series of serendipitous observations, in their eagerness to promote it, they have made some claims that are difficult to accept on face value. Of primary interest is the fact that azelaic acid, even in cell cultures, is not active against any cell lines until one approaches the 10-3 to