Antihistamine

Overview

What is Antihistamine?   

Antihistamines are a class of drugs commonly used to treat symptoms of allergies, such as runny nose, sneezing, itching, and watery eyes. They work by blocking the action of histamine, a substance in the body that causes allergic symptoms. 

Antihistamines, used as medication for hypersensitivity/allergies (H1-receptor antagonists), can be divided into two main categories: first-generation (sedating) and second-generation (non-sedating).

Global Name

• Generic name:  Diphenhydramine
• Brand names: Loratadine, Cetirizine and Fexofenadine

Usage

What is Antihistamine used for? 

Antihistamines are used to treat a variety of conditions, including: 

• Allergic rhinitis (hay fever) 

• Allergic conjunctivitis (eye allergies) 

• Urticaria (hives) 

• Reactions to insect bites and stings 

• Some forms of dermatitis and eczema 

• Allergy symptoms caused by chronic conditions such as sinusitis 

• Acute food allergies 

How do you use Antihistamine? 

Availability: 
Antihistamines are available in several forms, including tablets, capsules, liquids/syrup/solutions, nasal sprays, eye drops, and injectables. 

Dosage information: 

• Adults: Dosage varies depending on the specific antihistamine; refer to the product label or consult a healthcare provider. 

• Children: Dosage for children will depend on the child’s age and weight. Always consult a pediatrician before administering. 

• Elderlies: Lower doses may be necessary due to increased sensitivity or existing health conditions.

Are the following suitable to take the drug: Children, adults, elderlies? 

• Children: Yes, but dosage and form depend on age and weight. 

• Adults: Yes. 

• Elderlies: Yes, with caution and potential dosage adjustments. 

Is there anyone who can’t take Antihistamine? 

• Children: Very young children and infants should only use it under medical supervision. 

• Adults: Those with severe heart disease, urinary retention, or glaucoma should consult their doctor. 

• Elderlies: Use with caution; monitor for dizziness, sedation, and confusion. 

• Pregnancy: Consult a doctor as some antihistamines may be unsafe. 

• Lactation: Some antihistamines may pass into breast milk and could affect the infant. 

Allergies: People allergic to any specific antihistamine or the formulation’s components should avoid that particular drug. 

Warnings and precautions: First-generation antihistamines can cause drowsiness; avoid driving or operating heavy machinery. Alcohol can increase the sedative effects. 

Interactions and contraindications of the drug: 

• Antihistamines should be used cautiously with other CNS depressants like benzodiazepines and certain types of antidepressants. 
• Avoid using with other anticholinergic drugs as it may increase the risk of side effects. 

Side Effects

Common side effects include drowsiness, dry mouth, dizziness, and blurred vision. Less common but more serious side effects can include difficulty urinating, constipation, and confusion. 

Pharmacist Tips

• Storage information: Store at room temperature, away from direct sunlight and moisture. 

• Handling instructions: Keep antihistamines in their original packaging until use, and ensure caps are securely fastened to prevent moisture entry. 

Availability

Where is Antihistamines available in Hong Kong?

Antihistamines are over-the-counter (OTC) medications that can be sold without a prescription. They are found in all chain drug stores, including Mannings and Watsons. 

FAQs

Can I take Antihistamines every day?

Yes, many people take Antihistamines daily for chronic conditions. However, consult with a healthcare provider for long-term use. 

Do Antihistamines make you sleepy? 

First-generation Antihistamines can cause drowsiness. Second-generation Antihistamines are less likely to make you sleepy.

Can I take Antihistamines with alcohol?   

It is best to avoid alcohol as it can increase the sedative effects, especially with first-generation Antihistamines. 

How quickly do Antihistamines work?  

Most Antihistamines begin to work within 1 hour of intake, providing quick relief from allergic symptoms.