Anaphylaxis is an acute allergic reaction that occurs after a person has been injected with, or has eaten or inhaled, a substance to which he has previously been sensitized. This reaction, known also as anaphylactic shock, is brought about when the substance, called the antigen, reacts with antibodies that have previously been formed against it. Thus an injection containing a foreign protein may produce no ill effects the first time it is given; but the second time it is administered, anaphylaxis may occur. This happens because the person's produced antibodies against the foreign protein after the first injection.
Among the most common antigens that produce anaphylaxis are certain drugs, particularly antibiotics. Penicillin is a major offender, especially when it is given as an intramuscular injection.
Other common antigens include certain foods, such as shellfish; insect venoms, particularly those produced by bees, wasps, and ants; and certain serums, including horse serum. Whole blood plasma and gamma globulin also are frequent causes of anaphylaxis, as are egg powder and vaccines such as the flu vaccine, which are grown in chick embryos.
Animal danders and walnuts are also thought to be possible causes of anaphylaxis.
A person suffering anaphylaxis first becomes very pale and feels dizzy or faint. Soon, heart palpitations occur, accompanied by hives, a reddening of the face, and a drop in blood pressure. This condition is followed by a generalized edema, or swelling, which produces obstructions in the throat and lungs, causing a marked difficulty in breathing. Unless the victim is treated immediately, he may then enter a state of irreversible shock in which blood pressure falls drastically and death follows.
The treatment of anaphylactic shock begins with the administration of epinephrine (adrenalin) and cortisone derivatives. In many cases antihistamines also have been helpful, but any blood plasma or serum albumin should be given cautiously, since these substances may themselves be antigens.
The patient should always be placed in the position used in treating shock, with his head lower than his feet. Often it is necessary to administer oxygen and to create a pathway to the lungs by making an incision in the trachea.
A doctor can prevent anaphylaxis by finding out a patient's medical history and performing a skin test before injecting him with a particular drug. The doctor must be especially careful with patients who are known to have an allergy, such as hay fever, hives, or asthma. When administering penicillin, the doctor usually prescribes it in a form that can be taken by mouth. If it is necessary to inject the drug he carefully performs skin tests to observe the degree of wheal and flare reactions. In hospitals anaphylaxis caused by blood or plasma is prevented by cross-matching the blood before a transfusion is given.
For people who are known to have an allergic reaction to insect bites or stings, it is advisable to have a supply of the proper agents, such as cortisone sprays or tablets, in the medicine cabinet. It is sometimes possible to prevent anaphylaxis by desensitizing a person against a particular antigen.