diagnostic chemicals such as radiographic contrast media • foods, such as nuts and seafood • sulfite-containing food additives • insect venom, such as that from honeybees, wasps, and certain spiders 345 IMMUNE DISORDERS Treatment of allergic rhinitis involves controlling signs and symptoms and preventing infection. Treatment may include re- moving the environmental allergen. Drug therapy and immu- notherapy may be used to treat perennial allergic rhinitis. Annoying aftereffects Antihistamines, such as chlorpheniramine, diphenhydramine, and promethazine, are effective in stopping a runny nose and watery eyes, but they usually produce sedation, dry mouth, nausea, dizziness, blurred vision, and nervousness. Nonsedat- ing antihistamines, such as loratadine, desloratadine, fexofena- dine, and cetirizine, produce fewer annoying effects and have emerged as the treatment of choice. Try these treatments, too Topical intranasal corticosteroids may reduce local inflamma- tion with minimal systemic adverse effects. Cromolyn sodium may help prevent allergic rhinitis, but it takes 4 weeks to pro- duce a satisfactory effect and must be taken regularly during allergy season. Long-term management may include immunotherapy or de- sensitization with injections of allergen extracts administered preseasonally, seasonally, or every year. Battling illness Treating allergic rhinitis Anaphylaxis can result from contact with many common substances.
• a ruptured hydatid cyst (rare). Penicillin is the most common anaphylaxis-causing antigen. It induces a reaction in 4 out of every 10,000 patients. Reenacting the reaction Here’s how an anaphylactic reaction occurs: • After initial exposure to an antigen, the immune system re- sponds by producing IgE antibodies in the lymph nodes. Helper T cells enhance the process. • Antibodies bind to membrane receptors located on mast cells in connective tissues and on basophils, which are a type of leuko- cyte. • On reexposure, the antigen binds to adjacent IgE antibodies or cross-linked IgE receptors, activating inflammatory reactions such as the release of histamine. Untreated anaphylaxis causes respiratory obstruction, sys- temic vascular collapse, and death—minutes to hours after the first symptoms occur. However, a delayed or persistent reaction may last up to 24 hours. (See Treating anaphylaxis and Under- standing anaphylaxis .) 346 IMMUNE SYSTEM Anaphylaxis is always an emergency. It re- quires an immediate injection of epinephrine 1:1,000 aqueous solution, 0.1 to 0.5 ml, subcuta- neously (subQ) or I.M. If signs and symptoms persist, the injection should be repeated at 10- to 15-minute intervals as needed. Alternatively, 0.1 to 0.25 mg (1 to 2.5 ml of a 1:10,000 solution) may be given I.V. slowly over 5 to 10 minutes. The I.V. dose may be repeated every 5 to 15 minutes if needed or followed by an infusion at 1 to 4 mcg/minute. Diphenhydramine (Bena- dryl), 50 mg I.M. or I.V., may be given for aller- gic signs and symptoms. Aminophylline helps relieve bronchospasm.
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