There is no free xinafoic acid in the marketed product, Serevent
(GlaxoWellcome; Research Triangle Park, NC), or, indeed, any that is
formed in vivo at physiologic pH when the drug is
administered therapeutically. Extrapolations that the authors make with
regard to “clinically relevant concentrations of xinafoic acid” and
to agents “associated with occupational asthma” and “contribution
to fatalities” are erroneous and not justified.