ALLERGIC REACTION
A severe allergic reaction (anaphylaxis) can be life-threatening. It is caused by exposure to insect and animal venoms (such as wasp or jellyfish stings), plant products, medications, or any other agent to which the victim’s immune system has been previously sensitized.
Symptoms include low blood pressure (shock); difficulty breathing (severe asthma) with wheezing; swelling of the lips, tongue, throat, and vocal cords (leading to airway obstruction); itching; hives (red, raised skin welts that may occur singly or in large patches); nausea and vomiting; diarrhea; abdominal pain; seizures; and abnormal heart rhythms. Any or all of these symptoms may be present in varying severity. The most common life-threatening problem is respiratory distress. Facial swelling indicates that the airway may soon become involved. Be ready at all times to protect and support the airway.
TREATMENT FOR AN ALLERGIC REACTION
1. Administer aqueous epinephrine (adrenaline) 1:1,000 in a subcutaneous injection (see page 474). The adult dose is 0.3 to 0.5 mL; the pediatric dose is 0.01 mL/kg of body weight, not to exceed a total dose of 0.3 mL. For weight estimation, 1 kg equals 2.2 lb. The drug is available in preloaded syringes in certain allergy kits, which include the EpiPen autoinjector and EpiPen Jr. autoinjector (Dey), the Twinject autoinjector (Verus: 0.3 mg or 0.15 mg doses; 2 doses per unit), and the Ana-Kit. Instructions for use accompany the kits. The EpiPen and Twinject epinephrine products are generally easier for laypeople to use, because they require less dexterity to accomplish injection with them. The Twinject autoinjector and Ana-Kit syringe are configured with enough epinephrine for a second (repeat) dose, which is sometimes necessary. The Twinject is a true autoinjector for the first dose; the second dose is delivered as a routine injection from a concealed syringe and needle.
2. Administer diphenhydramine (Benadryl) by mouth. This is a histamine-1 receptor antagonist drug. A milder reaction that does not require epinephrine or corticosteroids may be managed with diphenhydramine alone. The adult dose is 50 to 75 mg every 4 to 6 hours; the pediatric dose is 1 mg/kg (2.2 lb) of body weight, also every 4 to 6 hours. The major side effect of this medication is drowsiness. A nonsedating antihistamine suitable for this purpose is fexofenadine (Allegra) 60 mg capsule for adults.
3. In case of a severe reaction, administer corticosteroids. Prednisone tablets in a dose of 50 to 80 mg should be given to an adult; the pediatric dose is 1 mg/kg (2.2 lb) of body weight. The onset of action of steroids is delayed for 4 to 6 hours; therefore, this drug should be given early in the course of therapy.
4. Administer an inhaled (aerosol or “micronized”) bronchodilator. Bronchodilators (airway openers) are drugs that have the advantages of minimal side effects and direct delivery to the site of action. They are available in metered-dose handheld nebulizers (“mistometers”) from which the victim inhales therapeutic puffs. An excellent drug for an acute attack is albuterol (Ventolin). The dose for an adult is two to six puffs initially, followed by two to four puffs every 3 to 6 hours. A child over age 12 who can manage the device may use a handheld nebulizer; younger children often require oral (liquid) medication in the appropriate dose.
5. Administer a histamine-2 receptor antagonist drug. This can be ranitidine (Zantac) 150 or 300 mg for an adult or famotidine (Pepcid) 10 or 20 mg for an adult.
