The antihistamine fexofenadine is generally well tolerated by patients with mostly minor side effects that can be treated by the patient or doctor. Many of these diminish as the body gets used to the medication over the course of treatment. Used to treat seasonal allergies and urticaria, or chronic hives, fexofenadine is sold under the trade name Allegra®. The most common fexofenadine side effects are vomiting and stomach upset, headache, coughing and diarrhea. Other frequently encountered side effects include respiratory tract infections, fatigue, dizziness and ear infection.
Most fexofenadine side effects are generally mild and treatable. Nausea or vomiting usually abate as the body acclimates to the medication, and are the most common side effects. Headache is reported almost as frequently as nausea and can be treated by the patient or doctor. If these side effects worsen or are severe, the patient is advised to let his or her healthcare provider know. Sufferers of allergic rhinitis or other problems using fexofenadine are also advised to let their doctors know if they experience any unexplained symptoms.
Other common fexofenadine side effects involve the respiratory tract and ears, and some patients have experienced an increase in infections in the middle ear and upper respiratory tract. Colds may be more frequent, and cases of the flu have been reported while taking the medication. Coughing and stuffy nose are other mild side effects.
Some rare but potentially dangerous reactions may require medical attention. A feeling of tightness in the chest or difficulty breathing might indicate a serious reaction to the medication. Another rarely reported side effect is the development of large swellings, primarily on the face, hands and feet. These hive-like bumps can also form inside the mouth and throat. Severe and recurring coughing or vomiting, excessive dizziness and fever are other rare fexofenadine side effects requiring medical attention.
Sleep disturbances and nightmares are more unusual fexofenadine side effects. Insomnia and fatigue during the day are some of the sleep irregularities reported. Some women have experienced painful menstrual periods while taking the medication. Nervousness has also been reported. During research studies on the medication, however, these rare symptoms occurred equally often with the medication or a placebo.
Unlike earlier forms of antihistamines, this medication does not easily cross the blood-brain barrier so severe drowsiness is not one of the common fexofenadine side effects. There have been very few cases of fexofenadine overdose. In animal studies, fatalities did not occur even with doses that were the equivalent of hundreds of times the recommended amount.