Antihistamines are a group of drugs that are effective in the treatment of allergic conditions such as hayfever, skin rash, hives and conjunctivitis, says the National Health Service in England. You get an allergic reaction when your immune system erroneously identifies an innocuous substance such as pollen as an invading organism and secretes a protein called histamine to defend the body against the attack. Histamine causes inflammation which leads to allergy symptoms such as red, swollen skin, sneezing, coughing and shortness of breath. Antihistamines prevent histamine from initiating the inflammatory response.
Loratadine (Claritin)
According to Drugs.com, loratadine is a histamine blocker that is available as a prescription and as an over-the-counter medication for the treatement of allergy symptoms. Adults and children 6 years of age and older take an oral dose of 10mg once a day. When you are taking loratadine, avoid alcoholic beverages and mediations such as sedatives and tranquilizers, says Drugs.com. Loratadine may cause drowsiness, so assess how your body responds to the drug before you drive or perform other tasks that require alertness. Other side effects include headache, nervousness, rapid heartbeat and dry mouth.
Diphenhydramine (Benadryl Allergy)
Diphenhydramine is a prescription and over-the-counter antihistamine that can treat allergy symptoms such as sneezing, runny nose, itching, watery eyes and rashes, says Drugs.com. For adults and children, the time interval between doses is 4 to 6 hours. Adults take 25 to 50mg per dose, children 2 to 6 years old take 6.25mg, and children 6 to 12 years old take 12.5 to 25mg. Get emergency medical help if you have a severe allergic reaction to diphenhydramine involving hives, swelling of the lips, tongue, or face, or closing of your throat. Less serious side effects include dizziness, sleepiness, headache, dry mouth and difficulty urinating.
Cetirizine (Zyrtec)
The Monthly Prescribing Reference describes cetirizine as an over-the-counter antihistamine that is suitable for the treatment of allergies and hayfever in adults and children. For children 2 to 6 years old, the oral dose is 2.5mg once a day, and if you are between 6 and 65 years old, you should take 5 to 10mg orally once a day. Avoid alcoholic beverages and medications such as sedatives and tranquilizers while you are taking cetirizine. If you are a nursing mother, you should not take this antihistamine, says the Monthly Prescribing Reference. Side effects include drowsiness, fatigue, dry mouth, sore throat, headache, diarrhea and irritability.
