AND THE ANSWERS ARE . . . A number of the more recent AH are effective in once daily dosing True All AH have the potential adverse side effect of triggering acute urinary obstruction in men with partial urinary outlet obstruction due to prostate hypertrophy False AH treatment in allergic rhinitis causes prominent relief of nasal obstruction False AH are the initial treatment of choice in mild persistent asthma False Some of the current AH have no adverse effects on driving and other cognitive activities True Comments A number of more recently developed AH such as fexofenadine 180 mg, desloratadine 10 and cetirizine 10 mg have relatively long durations of action so that they can be used just once daily. These agents are also much more specific than earlier AH (such as diphenhydramine) for blocking the receptors for histamine but not other receptors such as the cholinergic receptor. Therefore, treatment with these more recent AH do not have the potential of older AH such as diphenhydramine (Benadryl) to trigger acute urinary outlet obstruction due to blocking the cholinergic receptor. Treatment of allergic rhinitis with AH often reduces the nasal itching and sneezing. However, there is usually little if any reduction in the nasal congestion which is often very distressing to the patient. It is claimed that some of the most recently released AH have some decongestion effect. However, in my experience, this effect is quite modest, if present. For this reason, an oral decongestant agent, usually pseudoephedrine, is often used in combination with an AH agent in the treatment of allergic rhinitis. Although AH treatment has been shown to block some of the broncho-constrictive effect of inhaled histamine, AH treatment usually has very little direct beneficial effect on the lower airways in persistent asthma. Therefore, AH would not be an initial treatment of choice in persistent asthma. However AH may have some indirect beneficial effect in asthma by helping to control the allergic rhinitis which frequently accompanies persistent asthma. Several studies have suggested that control of allergic rhinitis is associated with improved control of concomitant asthma. The “non-sedating” AH fexofenadine in usual doses has no greater effect than placebo on driving capacity, reflexes, etc in double-blind studies using a driving simulator. In contrast, therapeutic doses of older AH such as diphenhydramine can adversely affect driving capacity as much as an alcoholic drink. References 1. N Engl J of Med- 2004;351:2203-2217 2. Allergy. 2004;59 Suppl 78:74-7 3. Allergy 2003;58: 192-197   Please tell us what you think of this site. © Copyright 1997-2008 American Academy of Allergy, Asthma & Immunology All rights reserved