Telfast Drug Interactions

Erythromycin and Ketoconazole: Fexofenadine HCl has been shown to exhibit minimal (ca. 5%) metabolism. However, co-administration of fexofenadine HCl with ketoconazole and erythromycin led to increased plasma levels of fexofenadine HCl. Fexofenadine HCl had no effect on the pharmacokinetics of erythromycin and ketoconazole. In 2 separate studies, fexofenadine HCl 120 mg twice daily (2 times the recommended twice-daily dose) was co-administered with erythromycin 500 mg every 8 hrs or ketoconazole 400 mg once daily under steady-state conditions to normal, healthy volunteers (n=24, each study). No differences in adverse events or QTc interval were observed when patients were administered fexofenadine HCl alone or in combination with erythromycin or ketoconazole. The findings of these studies are summarized in Table 4. (See Table 4.)

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The changes in plasma levels were within the range of plasma levels achieved in adequate and well-controlled clinical trials.
The mechanism of these interactions has been evaluated in in vitro, in situ and in vivo animal models. These studies indicate that ketoconazole or erythromycin co-administration enhances fexofenadine gastrointestinal absorption. In vivo animal studies also suggest that in addition to increasing absorption, ketoconazole decreases fexofenadine HCl gastrointestinal secretion, while erythromycin may also decrease biliary excretion.
Omeprazole: No fexofenadine-omeprazole interaction was observed.
Antacids: Administration of fexofenadine HCl 120 mg (2 x 60-mg cap) within 15 min of an aluminum- and magnesium-containing antacid (Maalox) decreased fexofenadine AUC by 41% and C_max by 43%. Telfast should not be taken closely in time with aluminum- and magnesium-containing antacids. A period of approximately 2 hrs between the administration of fenofexadine HCl and antacid should be maintained.
Oral suspension: The concomitant administration of TELFAST (ORAL SUSPENSION) with erythromycin or ketoconazole did not demonstrate any significant increase in the QTc interval. No difference in adverse effects was reported when these agents were administered alone or combined.
No fexofenadine-omeprazole interaction was observed. However, the administration of an antacid containing aluminum hydroxide and magnesium, approximately 15 minutes before taking fexofenadine hydrochloride reduced bioavailability. A period of approximately two hours between the administration of fexofenadine hydrochloride and antacids that contain aluminum hydroxide and magnesium should be maintained.