Anaphylaxis or anaphylactic reaction. This is a serious allergic reaction that can be life threatening. A person with anaphylaxis must be treated in a hospital emergency department.

Almost all anaphylactic reactions occur within four hours of the first dose of the drug. Most occur within one hour of taking the drug, and many occur within minutes or even seconds.

Always contact the health-care provider who prescribed the medication for advice. If the symptoms are mild, such as itching and localized hives, the provider may switch you to a different type of medication, recommend that you stop the medication, or, if appropriate, prescribe antihistamines to relieve your symptoms.

If you cannot reach this provider for advice quickly, play it safe and go to a hospital emergency department.

If you are having any "systemic" symptoms such as fever or vomiting, you should stop taking the medication and be seen immediately by a medical professional.

If you are having difficulty breathing, your throat is swelling, or you are feeling faint, you may be having an anaphylactic reaction. Go immediately to a hospital emergency department. Do not attempt to drive yourself. If no one is available to drive you right away, call 911 for an ambulance. While waiting for the ambulance, start self-treatment.

Generally a drug allergy is identified by signs and symptoms. Medical professionals are trained to recognize hives, swelling patterns, and rashes associated with allergic reactions. You will be asked questions about your medical history and possible triggers of the reaction.

Blood tests and other tests are needed only under very unusual circumstances. After getting advice from your health-care provider, some mild allergic reactions may be treated at home.

For hives or localized skin reactions, perform the following: take cool showers or apply cool compresses. Wear light clothing that doesn't irritate your skin. Take it easy. Keep your activity level low. To relieve the itching, apply calamine lotion or take nonprescription antihistamines, such as diphenhydramine (Benadryl) or chlorpheniramine maleate (Chlor-Trimeton).

For more severe reactions, self-treatment is not recommended. Call your health-care provider or 911, depending on the severity of your symptoms.

Always contact the health-care provider who prescribed the medication for advice. If the symptoms are mild, such as itching and localized hives, the provider may switch you to a different type of medication, recommend that you stop the medication, or, if appropriate, prescribe antihistamines to relieve your symptoms.

If you cannot reach this provider for advice quickly, play it safe and go to a hospital emergency department. If you are having any "systemic" symptoms such as fever or vomiting, you should stop taking the medication and be seen immediately by a medical professional.

If you are having difficulty breathing, your throat is swelling, or you are feeling faint, you may be having an anaphylactic reaction. Go immediately to a hospital emergency department. Do not attempt to drive yourself. If no one is available to drive you right away, call 911 for an ambulance. While waiting for the ambulance, start self-treatment.