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What Is a Second Generation Antihistamine?

Between 40 and 50 million Americans suffer from allergies, according to the American Academy of Allergy, Asthma and Immunology. The most common treatment and prevention for allergic reactions is the use of second-generation antihistamines. Second-generation antihistamines are the most effective at treating seasonal allergies. They reduce the common symptoms of an allergic reaction such as watery eyes, sneezing and a runny nose.

  1. Definition

    • Antihistamines are separated into two categories: first-generation and second-generation. First-generation antihistamines are older, more powerful drugs noted for their sedating side effects, according to familydoctor.org. Second-generation antihistamines are newer drugs, typically sold in 24-hour doses, and do not cause drowsiness in a healthy adult.

    Function

    • The function of second-generation antihistamines is to prohibit the body from releasing high levels of histamine in the blood. When you experience an allergic reaction, your immune system releases antibodies and histamine to fight off the allergen. The histamine levels in the body produces common allergy symptoms. Second-generation antihistamines are preferred because they do not cause drowsiness. This is attributed to the fact that these drugs do not cross the brain-blood barrier (first-generation antihistamines do). Taking a second-generation antihistamine can prevent and treat most seasonal allergies.

    Types

    • Three types of second-generation antihistamines are available for purchase, according to, The American Academy of Family Physicians. Two of the second-generation antihistamines are available over the counter--loratadine or Claritin and cetirizine or Zyrtek--and the last is available by a doctor's prescription--fexofenadine or Allegra. All three drugs are available in a single, 24-hour dose.

    Dose

    • Loratadine is administered at 10mg daily for adults and takes one to three hours for the drug to take effect. Cetirizine is taken orally at five to 10mg daily for adults, taking 15 to 30 minutes before the drug takes effect. Fexofenadine is typically given in 60mg doses once to twice daily for adults, taking one hour for the drug to take effect, according to The American Academy of Family Physicians.

    Considerations

    • Before taking an antihistamine, talk to your doctor. If you are taking any other drugs, an antihistamine may have a negative drug interaction. The most common adverse drug interactions with second-generation antihistamines are sedatives, sleeping pills and muscle relaxants, according to familydoctor.org. Many over-the-counter cold and sinus medications contain an antihistamine. Check the ingredients and consult with a pharmacist or doctor before combining multiple cold and sinus medications. If your allergy symptoms do not improve with the use of second-generation antihistamines, see an allergist for a specific diagnosis.

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