Fexofenadine hydrochloride

Some of the views expressed in the following notes on newly approved products should be regarded as preliminary, as there may have been limited published data at the time of publication, and little experience in Australia of their safety or efficacy. However, the Editorial Executive Committee believes that comments made in good faith at an early stage may still be of value. Before new drugs are prescribed, the Committee believes it is important that more detailed information is obtained from the manufacturer's approved product information, a drug information centre or some other appropriate source.

Telfast (Hoechst Marion Roussel)
60 mg capsules

Indication: seasonal allergic rhinitis
There have been concerns about potentially fatal interactions between terfenadine and drugs such as erythromycin. While there has been debate about the mechanism of the interaction1, this new product aims to overcome the concerns.

Fexofenadine is a metabolite of terfenadine which is being marketed as a non-sedating antihistamine without the risks of the parent compound. One capsule can be taken up to twice a day for the relief of symptoms.

The drug has a bioavailability of 33%, but the effect of food appears not to be clinically significant. Most of the drug is excreted unchanged in the urine with a terminal elimination half-life of 11-16 hours. The pharmacokinetics are significantly affected by interactions with erythromycin and ketoconazole; however, these changes are not believed to increase the incidence of adverse effects.

The adverse effects of fexofenadine include headache, nausea, drowsiness and fatigue. Although fexofenadine seems to be well tolerated, health professionals should be aware that its approval was based on studies of two weeks' duration.

Fexofenadine will reduce the symptoms of seasonal allergicrhinitis. The antihistamine effect begins within an hour of taking the tablet and peaks after 6 hours. The effectiveness of fexofenadine relative to other antihistamines is unknown.