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Editor, – We are contacting you out of concern for your comments regarding fexofenadine hydrochloride ('New drugs' Aust Prescr 1997;20:48) and, in particular, the sentence advising health professionals that 'its approval was based on studies of two weeks' duration'.
This statement is incomplete and thus misleading. The approval of fexofenadine, the active metabolite of terfenadine, with no restriction to its duration of use, was based on the two-week efficacy studies to which you refer, as well as on the extensive data available from experience with terfenadine. Every patient who has taken terfenadine has been exposed to fexofenadine and thus the duration of exposure of the public to this molecule is actually far greater than two weeks.
Further addition to your article is required:
- Fexofenadine is the active metabolite of terfenadine; it requires no metabolic activation.
- Increases in fexofenadine levels in the presence of ketoconazole and erythromycin are associated with absorption interference rather than hepatic metabolism interference. In any case, fexofenadine has no inherent cardiac toxicity.
Michael Smith
Regulatory Project Manager
Hoechst Marion Roussel
Lane Cove, N.S.W.
