To the Editor: The Research Letter by Dr Nyirenda and colleagues1 demonstrated that cigarette smokers compared with nonsmokers showed a much slower reduction in concentrations of thyroid-stimulating hormone (TSH)–receptor antibody, free thyroxine (FT4), and total triiodothyronine (T3) with carbimazole treatment. Smokers required higher doses of carbimazole than nonsmokers. As possible causes for these results, the authors speculated about several factors such as kinetic variability among individuals; the effect of smoking on carbimazole absorption, concentration in the thyroid gland, or metabolism; and the effect of smoking on expression of microsomal enzymes, which could influence the concentration of carbimazole or its metabolites.
Shin JI, Lee JS. Carbimazole Treatment in Smokers vs Nonsmokers With Graves Disease. JAMA. 2009;301(19):1988-1989. doi:10.1001/jama.2009.556