What are the types of antihistamines (anti-histamine medications)?

From the Guidelines

Antihistamines are classified into two main types: first-generation and second-generation antihistamines, with second-generation antihistamines being generally preferred due to their minimal sedation and fewer side effects 1. There are several key differences between these two types of antihistamines.

• First-generation antihistamines, such as diphenhydramine, hydroxyzine, and clemastine, are associated with sedative effects, including drowsiness and performance impairment, as well as anticholinergic effects like dry mouth and constipation 1.
• Second-generation antihistamines, including cetirizine, loratadine, fexofenadine, desloratadine, and levocetirizine, cause minimal sedation and have fewer side effects, making them a better choice for daily use 1. Some important considerations when choosing an antihistamine include:
• The specific symptoms being treated, such as allergic rhinitis or urticaria
• The timing of relief needed, with first-generation options potentially working faster for acute reactions
• The need for daytime alertness, with second-generation antihistamines being a better choice for ongoing management
• Potential interactions with other medications, such as sedatives or antidepressants, which can enhance performance impairment from antihistamines 1. It's also worth noting that some second-generation antihistamines, like cetirizine and intranasal azelastine, may cause sedation at recommended doses, while others like fexofenadine, loratadine, and desloratadine do not cause sedation at recommended doses 1. In general, second-generation antihistamines are preferred for their effectiveness and safety profile, with minimal sedation and fewer side effects, making them a better choice for daily use 1.

From the FDA Drug Label

Fexofenadine hydrochloride, the major active metabolite of terfenadine, is an antihistamine with selective peripheral H1-receptor antagonist activity. There are two main types of antihistamines mentioned indirectly in the provided drug labels:

• H1-receptor antagonist: This type is directly mentioned in the context of fexofenadine hydrochloride 2 No conclusion can be drawn regarding other types of antihistamines, as the provided drug labels do not explicitly address this question.

From the Research

Types of Antihistamines

• Non-sedating antihistamines: These are recommended for the treatment of allergies such as pollinosis and atopic dermatitis because of their low penetration into the central nervous system 3.
• Sedating antihistamines: These can cause drowsiness and are not needed for long-term itching, as glucocorticoids are indicated and more effective 4.
• First-generation antihistamines: These produce some degree of drowsiness, as well as anticholinergic side effects 5.
• Second-generation antihistamines: These are less likely to produce sedation and include loratadine, cetirizine, and fexofenadine 6.

Examples of Antihistamines

• Acrivastine
• Astemizole
• Cetirizine
• Desloratadine
• Ebastine
• Fexofenadine
• Levocetirizine
• Loratadine
• Mizolastine
• Terfenadine 4, 7

Classification of Antihistamines

• Antihistamines can be classified into three categories: sedating, less-sedating, and non-sedating antihistamines according to their sedative effects 3.
• Brain H1 receptor occupancy measurements can be used to classify antihistamines objectively into these categories 3.