Terfenadine is a highly effective but dangerous antihistamine
remedy for hayfever
(seasonal allergic rhinitis
). It is or was made by Hoechst Marion Roussel
(Merrell Dow) under the brand name Seldane
. Another brand is Triludan
. When overdosed on, it can cause fatal cardiac arrhythmia
. It is a tiny white pill, so if you take your one-a-day pill in the morning and a couple of hours later forget whether you've taken it, taking a second one is getting close to a potentially toxic overdose
It is strongly amplified by grapefruit juice. Many common medications are highly dangerous when taken with grapefruit juice. It also reacts badly with numerous other medicines, of course, but not mixing these is common sense.
Hoechst Marion Roussel have developed an alternative, fexofenadine, under the brand names Allegra and Telfast, which has similar effect to terfenadine on hayfever but does not cause cardiac arrhythmia and does not have adverse reaction with grapefruit juice.
Terfenadine is now withdrawn in Britain, and is prescription-only in Canada. A move to withdraw it in the USA in 1997 was resisted by the manufacturer, who said the answer was education in correct use. The antihistamines astemizole and loratadine are reported to have similar problems, though not as strongly as terfenadine.