Fexofenadine (Allegra, and others) is the most recent second-generation H1-antihistamine to become available over the counter (OTC). Cetirizine (Zyrtec, and others) and loratadine (Claritin, and others) are already available OTC. Cetirizine can be sedating in usual doses. Loratadine can be sedating in higher-than-usual doses. Fexofenadine remains nonsedating even in higher doses.1
The manufacturer of Zyrtec has responded to this new OTC product with television advertisements drawing attention to the label warning against taking fexofenadine with fruit juice. Many fruit juices such as grapefruit, orange and apple juice are organic anion transporting peptide (OATP) 1A2 inhibitors. OATP1A2 transporters are involved in the absorption of fexofenadine from the gastrointestinal tract. Inhibition of the activity of intestinal OATP1A2 reduces serum concentrations of fexofenadine by up to 70%, possibly reducing its effectiveness.2 Patients can avoid this interaction by not drinking fruit juice within 4 hours before or 1-2 hours after taking fexofenadine.