Fexofenadine or Allegra is a non-sedating antihistamine. It is the active metabolite of another non sedation antihistamine - terfenadine.
Fexofenadine or Allegra blocks histamine sites, specifically histamine 1 sites, to prevent the release of histamine and its symptoms - runny nose, watery eyes, sneezing.
Being a non-sedation antihistamine, in the recommended doses, Fexofenadine or Allegra does not cause drowsiness. It does not have anticholinergic side effects such as dry mouth.
Because Fexofenadine or Allegra is excreted through the kidneys, people with poor kidney functioning need lower doses.
It does not in combination with antibiotics such as erythromycin cause heart beat irregularities.
Med Letter 1996;38(986):95
The relevant product monographs must be regarded as the appropriate sources of prescribing information.