From the Guidelines
The antihistamine with the soonest onset of action is nasal azelastine, which has been reported to have a clinically significant onset of action at 15 minutes. This is based on a study published in the Journal of Allergy and Clinical Immunology 1. When considering the onset of action, it's essential to weigh the benefits of quick relief against potential side effects, such as sedation. Nasal azelastine is a topical antihistamine, which may have a faster onset of action compared to oral antihistamines.
- Key points to consider:
- Nasal azelastine has a rapid onset of action, making it a good option for patients who need quick relief from allergic rhinitis symptoms.
- The recommended dosing for nasal azelastine is 2 sprays in each nostril twice daily for patients 12 years of age and older.
- Common side effects of nasal azelastine include bitter taste (19.7% of patients) and somnolence (11.5% of patients) 1.
- In comparison to other antihistamines, nasal azelastine has a faster onset of action than nasal olopatadine, which has an onset of action of 30 minutes 1. Oral antihistamines like cetirizine and fexofenadine may have a slower onset of action, typically ranging from 20-120 minutes.
- It's crucial to consider the potential for sedation when choosing an antihistamine, as some antihistamines like cetirizine and intranasal azelastine may cause sedative properties, especially at higher doses or in certain individuals 1.
From the FDA Drug Label
CLINICAL PHARMACOLOGY: ... Diphenhydramine hydrochloride in the injectable form has a rapid onset of action. The antihistamine with the soonest onset is diphenhydramine (IV), due to its rapid onset of action 2.
From the Research
Antihistamine Onset of Action
- The onset of action of antihistamines can vary depending on the specific medication and individual response 3, 4.
- Diphenhydramine is often considered to have a rapid onset of action, but its use is limited by its sedative effects and other adverse reactions 3, 4, 5.
- Cetirizine has been reported to have the fastest onset of action among the newer antihistamines, making it a potential option for acute allergic reactions 4.
- Fexofenadine has a slower onset of action compared to diphenhydramine and cetirizine, but it does not impair psychomotor or cognitive skills and shows no dose-related increase in sedation 3, 4, 6.
- Levocetirizine may have a greater in vivo H1 receptor occupancy compared to other second-generation antihistamines, which could confer an advantageous efficacy/safety profile 6.
Comparison of Antihistamines
- Second-generation antihistamines, such as cetirizine, desloratadine, fexofenadine, levocetirizine, and loratadine, have reduced CNS effects and are considered safer than first-generation antihistamines like diphenhydramine 4, 6, 5.
- The choice of antihistamine depends on various factors, including the specific condition being treated, individual patient response, and potential side effects 3, 4, 6, 5, 7.