Zyban: Two Products, Two Uses—Too Confusing?

To the Editor.—Physicians should be alerted to the unfortunate choice of names for the smoking cessation drug, Zyban or bupropion hydrochloride. Zyban (Grace-Sierra Co, Malpitas, Calif) is also the trade name for thiophanate with mancozeb, one of the few fungicides still approved and widely used in many areas of the United States for residential and nursery applications (Figure 1). An active metabolite of Zyban (for horticulture use) is a benzimidazole that binds β-tubulin and inhibits microtubule function. The benzimidazoles bind only weakly to mammalian tubulin, but nevertheless have been classified as potential human carcinogens based on animal studies.^{1 - 2} Mancozeb, a dithiocarbamate fungicide, has both mutagenic and teratogenic properties.^{3 - 4}

In my academic-based clinic, with a largely referral population from rural, northern Florida, I have already had patients express surprise that I would recommend a product for smoking cessation that was originally intended for agricultural use. Worse still, most agricultural workers will be aware that benzimidazoles also have been widely used as antihelminthic drugs in animals, so an extension to human use might be anticipated. Given the large number of people who seek economy in medications by obtaining prescription drugs from nonphysician sources, and the even larger number of people exposed to the advertising blitz directed at the general public by the manufacturer of the pharmaceutical Zyban, it is possible that some patients will find the fungicide, Zyban, conveniently sitting on a shelf with their other out-of-reach gardening, pesticide, and veterinary supplies, and use it as a substitute for bupropion.