Typically, it is not recommended to use loratadine (Claritin) and fexofenadine (Allegra) at the same time. Both medications are second-generation antihistamines used for allergy relief. Taking them together would not provide much added benefit, but could lead to side effects such as drowsiness.
Flonase As An Alternative
Another option, beside taking Claritin and Allegra together, would be to switch or add fluticasone (Flonase) nasal spray. Flonase was approved by the FDA in 1990, but has only been available over-the-counter since 2014. Flonase is a type of steroid that blocks inflammation, itching, and congestion.
According to the, it has some advantages over Claritin including working better for nasal congestion. Flonase can be used once daily with 1 or 2 sprays into each nostril or may be used as needed instead of every day.
Zyrtec As An Alternative
Another antihistamine that could be tried instead is cetirizine (Zyrtec). In some patients, Zyrtec may work better, however, it also may also cause drowsiness. Zyrtec, Claritin, and Allegra are second-generation antihistamines and are still less likely to cause drowsiness than first-generation antihistamines such as Benadryl (diphenhydramine). This is because first-generation antihistamines cross the blood-brain barrier, whereas the second-generation antihistamines usually do not.
How Antihistamines Work
Antihistamines bind to histamine receptors that are found in the nose, lungs, eyes, and skin without activating the histamine response. By binding and changing the shape of the histamine receptor, antihistamines inhibit histamine from binding and creating its response. Histamine creates an immune response to essentially attempt to remove the offensive allergen.
Histamine can be triggered by a variety of things including pollen, dust, and pet dander. Some people are more sensitive to this response and may not even know what triggers their allergies. Antihistamines are useful in preventing the immune cascade so common in people suffering from allergies.
To conclude, it is not recommended to take both Claritin and Allegra together due to the possibility of drowsiness without additional benefit. Another antihistamine that could be considered is Zyrtec, but may slightly increase the chance of drowsiness. Finally, Flonase nasal spray may be another option to provide another mechanism of action against allergies.