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  • Q&A with Australian Health Practitioners

    What are the long term effects of taking antihistamines?

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  • 1




    The role of the Eczema Association of Australasia Inc (EAA) is to be a supportive body for eczema sufferers and carers, to increase public awareness … View Profile

    Antihistamines are typically separated into sedating (first generation) and nonsedating (second generation) forms, based upon their central nervous system effects, the nonsedating agents being less likely to cross the blood-brain barrier.  In addition, some antihistamines have additional anticholinergic, antimuscarinic or other actions.  Antihistamines are some of the most commonly used drugs in medicine, and most are available in multiple forms, both by prescription and in over-the-counter products, alone or combined with analgesics or sympathomimetic agents.  Common uses include short term treatment of symptoms of the common cold, seasonal allergic rhinitis (hay fever), motion sickness, nausea, vertigo, cough, urticaria, pruritus and anaphylaxis.  Sedating antihistamines are also used as mild sleeping aids and to alleviate tension and anxiety.  Many antihistamines are also available in topical forms, as creams, nasal sprays and eye drops for local use in alleviating allergic symptoms.  Nonsedating antihistamines are typically used in extended or long term treatment of allergic disorders, including allergic rhinitis (hay fever), sinusitis, atopic dermatitis, and chronic urticaria.

    Antihistamines have several adverse side effects which are related to their antihistaminic actions.  Side effects are, however, usually mild and rapidly reversed with stopping therapy or decreasing the dose.  These common side effects include sedation, impaired motor function, dizziness, dry mouth and throat, blurred vision, urinary retention and constipation.  Antihistamines can worsen urinary retention and narrow angle glaucoma.

    Antihistamines rarely cause liver injury.  Their relative safety probably relates to their use in low doses for a short time only.  The nonsedating antihistamines, however, are often used for an extended period and several forms have been linked to rare instances of clinically apparent acute liver injury which has generally been mild and self-limiting; the antihistamines most commonly linked to liver injury have been cyproheptadine, cetirizine and terfenadine (which is no longer in clinical use).

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    Prof Rodney Sinclair

    Dermatologist (Skin Specialist)

    Professor Sinclair is a Professor of Dermatology at the University of Melbourne and Director of Sinclair Dermatology. He is past-president of the Australasian Society for … View Profile

    Antihistamines are mainly used to control urticaria and heyfever.  If you have urticaria that is not well controlled by antihistamines consider seeing a dermatologist for assessment and treatment advice.,-diagnosis-and-management-of-chronic-urticaria/

    If you have severe and persitant urticaria, you may consider enrolling in a clinical trial.

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    Dr Alexander Lozynsky

    Allergy Specialist & Immunologist

    Consultant allergist and immunologist, with particular interest in allergic rhinitis and sinusitis, allergic respiratory disorders, food allergies and sensitivity and allergic skin conditions, including atopic … View Profile

    Antihistamines are helpful in controlling allergic respiratory and skin conditions. It is important to remember that they act by blocking H1 receptors from histamine, which is released from mast cells and other cells in the body. Therefore, it is more effective to take them before an allergic reaction occurs, as they cannot displace histamine already attached to receptors. So, before mowing the grass if you are allergic to grass pollen or visiting friends who have a cat if you are allergic to cat dander. 

    Non-sedating antihistamines can be helpful in controlling symptoms from ingesting foods and drinks, especially red wine, that are high in amines, including MSG (monosodium glutamate). Again, for maximum effect, they need to be taken before having these foods and drinks. 

    The dose of antihistamine is also important, as the recommended dose of one tablet may be sufficient to control symptoms of allergic rhinitis and conjunctivitis, but higher doses are usually required to control urticaria. When one class of antihistamine becomes less effective it is worthwhile trying another type.

    Although it is preferable to recommend non-sedating antihistamines, in allergic skin disorders of eczema and urticaria where itching can be quite distressing and affect sleep, the addition of a sedating antistamine can be beneficial.  

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