Antihistamines: Functions, Varieties, and Potential Adverse Reactions

Antihistamines: Functions, Varieties, and Potential Adverse Reactions

Antihistamines are a common medication used to treat allergy symptoms, motion sickness, and some cold and flu symptoms. These medications work by blocking the action of histamine, a substance that the body releases during an allergic reaction, causing symptoms such as congestion, sneezing, runny nose, itchy or watery eyes, itching skin, rash, hives, and nausea.

However, not all antihistamines are created equal. They can be categorised into three generations, each with its unique characteristics and effects.

First-generation antihistamines, including diphenhydramine (Benadryl) and chlorpheniramine (Chlor-Trimeton), are known for being quick-acting and effective. Unfortunately, they easily cross the blood-brain barrier and affect H1 receptors in the central nervous system (CNS), leading to sedation, drowsiness, and fatigue. Additionally, these antihistamines have anticholinergic effects, causing side effects such as dry mouth, dizziness, and potential for falls, especially in the elderly.

Second-generation antihistamines, such as loratadine, cetirizine, and fexofenadine, are more selective for peripheral H1 receptors and do not cross the blood-brain barrier significantly, thus minimising sedation and CNS effects. This makes them safer for daily use and children, and they are preferred for chronic allergy management, such as seasonal allergic rhinitis and chronic urticaria.

Third-generation antihistamines are newer derivatives aimed at further improving safety profiles and minimising CNS penetration. They are largely non-sedating and appropriate for long-term allergy treatment. Examples of third-generation antihistamines include desloratadine, rupatadine, and bilastine.

When choosing an antihistamine, it is essential to consider the specific symptoms being treated, the age of the individual, and the frequency of use. Second- or third-generation antihistamines are generally preferred for managing chronic allergy symptoms, especially in children or individuals needing to avoid drowsiness. First-generation agents may be reserved for short-term or specific symptomatic use with caution.

Parents and caregivers should consult a healthcare professional before giving an antihistamine to a child, especially if the child is 12 years old or younger. Over-the-counter antihistamines are available in forms such as tablets, gel capsules, nasal sprays, and eye drops.

It is crucial to note that while second- and third-generation antihistamines are safer and more potent than the first-generation types, long-term use of non-sedating antihistamines may result in mild liver damage. Terfenadine, associated with liver damage, is no longer available for clinical use.

Pregnant women can generally take low doses of first- and second-generation antihistamines, but high doses of promethazine may cause adverse side effects during pregnancy. If a person suspects an overdose on antihistamines, they should seek immediate medical attention or call the American Association of Poison Control Centers (AAPCC) for advice at 1-800-222-1222.

In conclusion, understanding the differences between first-, second-, and third-generation antihistamines can help individuals make informed decisions about their allergy treatment. Always consult a healthcare professional for personalised advice and guidance.

1. Some allergy symptoms, like congestion and sneezing, can be addressed with antihistamines.
2. Antihistamines are also used for motion sickness and certain cold and flu symptoms.
3. These medications block the action of histamine, a substance that triggers allergic reactions.
4. First-generation antihistamines, such as Benadryl and Chlor-Trimeton, have quick-acting effects.
5. Unfortunately, they also quickly cross the blood-brain barrier, affecting the central nervous system (CNS).
6. This leads to sedation, drowsiness, and fatigue with the use of first-generation antihistamines.
7. They also have anticholinergic effects, causing side effects like dry mouth and dizziness.
8. Elderly individuals are particularly susceptible to falls due to the anticholinergic effects of first-generation antihistamines.
9. Second-generation antihistamines, like loratadine and cetirizine, are more selective for peripheral H1 receptors.
10. This minimizes sedation and central nervous system (CNS) effects, making them safer for daily use and children.
11. Second-generation antihistamines are effective for managing chronic allergy symptoms, such as seasonal allergic rhinitis and chronic urticaria.
12. Third-generation antihistamines are aimed at further improving safety profiles and minimizing CNS penetration.
13. Examples of third-generation antihistamines include desloratadine, rupatadine, and bilastine.
14. When choosing an antihistamine, consider the specific symptoms being treated and the age of the individual.
15. Second- or third-generation antihistamines are generally preferred for managing chronic allergy symptoms, especially in children.
16. First-generation agents may be reserved for short-term or specific symptomatic use with caution.
17. Parents and caregivers should consult a healthcare professional before giving an antihistamine to a child, especially those under 12.
18. Over-the-counter antihistamines come in various forms, such as tablets, gel capsules, nasal sprays, and eye drops.
19. Long-term use of antihistamines may result in mild liver damage, as seen with terfenadine, which is no longer available clinically.
20. Pregnant women can generally take low doses of first- and second-generation antihistamines, but high doses of promethazine may cause adverse side effects.
21. In case of an antihistamine overdose, seek immediate medical attention or call the American Association of Poison Control Centers (AAPCC) at 1-800-222-1222.22.It's important to understand the differences between first-, second-, and third-generation antihistamines to make informed decisions about allergy treatment.
22. Always consult a healthcare professional for personalised advice and guidance.
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