Drug allergies arise from a complicated response by the immune system to a speciﬁc medication. A person usually goes through three stages when develop- ing an allergy to a medication. First, he or she must be exposed to the drug by taking one or more doses. Next, the person’s immune system identiﬁes the drug as harmful and begins producing antibodies to ﬁght it. Finally, the person takes another dose of the drug, and the allergy symptoms appear. The symptoms may appear immediately, within 1 to 2 hours, or within a few days to a week after taking the drug. Common symptoms of drug allergy include skin rash or hives, difﬁculty breathing, and itching. Severe drug allergies may cause seizures, loss of consciousness, or shock (see box below). If you have had a previous severe allergic reaction, you will need to carry an injecting device that contains epinephrine with you at all times, so you can inject yourself immediately if you have another allergic reaction. An injection of epinephrine can save your life.
Anaphylactic shock is a severe, life-threatening allergic reaction. The reaction usually occurs after an insect sting or bite or after injection of a speciﬁc drug such as peni- cillin. Occasionally the reaction occurs after eating a particular food or taking a speciﬁc medication. Anaphylactic shock is a medical emergency that requires immediate medical treatment.
During an anaphylactic reaction, the body releases massive amounts of histamine and other powerful chemicals in response to the presence of the allergen. The blood vessels widen, causing a sudden, severe decrease in blood pressure. Other symptoms can include hives (itchy, raised, red patches on the skin); swelling of the lips, tongue, and throat; abdominal pain; diarrhea; and difﬁculty breathing due to bronchospasm (narrowing of the airways in the lungs).
If you or someone you know has an anaphylactic reaction, call 911 or your local emer- gency number. While waiting for emergency help to arrive, have the person lie down, with face up, head low, and legs raised about a foot high to improve blood ﬂow to the upper body. An injection of epinephrine is needed as soon as possible to counteract the allergic reaction. If you or the person has had a severe allergic reaction before and carries an injecting device that contains epinephrine, use it as soon as symptoms appear.
Medications that typically produce an allergic reaction include antibiotics (such as penicillin), sulfa drugs, insulin that contains pig or ox protein, vaccines, and aspirin. If you are allergic to any medications, be sure to tell your doctor and other healthcare providers who are treating you, such as a nurse or a dentist. Also, in case of emergency, you should always wear a medical identiﬁcation bracelet or necklace and carry a wallet card that informs people of your allergy. This will help ensure appropriate medical treatment.
Warning Signs of Allergy to Medication
Always report any unpleasant or unexpected side effects of medication to your doctor.
The following symptoms may indicate an allergy to medication:
• hives (itchy, raised, red patches on the skin)
• swollen lips
If you experience any of these symptoms after taking medication, contact your doc- tor. If you experience more serious symptoms—such as nausea and vomiting, difﬁculty breathing, confusion, loss of consciousness, swollen tongue or throat, or slurred speech—seek emergency medical help immediately. A severe allergic reaction is a med- ical emergency that can lead to respiratory failure and shock (see “Anaphylactic Shock,” previous page).
Allergies to Food
A food allergy is a reaction of the immune system to a food or food ingredient that most people ﬁnd harmless. If you eat a food that produces an allergic reac- tion, your immune system responds by releasing numerous chemicals that cause allergic symptoms. A food allergy is different from a food intolerance, which does not trigger an immune response. A food intolerance (such as lactose intol- erance, see page 266) usually arises from an enzyme deﬁciency and produces symptoms such as stomach cramps, gas, or diarrhea. Food intolerances are rela- tively common, but a true food allergy is rare, affecting only about 1 percent of the population.
The most common foods that cause allergies in adults are ﬁsh and shellﬁsh, eggs, and nuts—such as peanuts, walnuts, and pecans. Symptoms of food allergy can include skin reactions such as hives or rashes, nasal congestion, asthma attacks (see page 245) in people who have asthma, and gastrointestinal problems such as nausea, gas, or diarrhea. Because both food allergies and food intoler- ances can cause intestinal symptoms, the two disorders are easily confused and must be diagnosed by a doctor.
Food allergy symptoms can appear immediately after eating or may develop over time—within hours or even days. In severe cases the food can provoke a serious reaction known as anaphylaxis (see “Anaphylactic Shock,” previous page), which can be life-threatening. Signs and symptoms of anaphylaxis include hives, difﬁculty breathing, a drop in blood pressure, and loss of consciousness.
To determine whether you have a true food allergy, your doctor probably
will perform one of two tests: a skin prick test or a blood test called the radio- allergosorbent test (RAST). During the skin prick test, the doctor deposits a small amount of the suspected food allergen onto your forearm and then pricks the skin beneath it with a needle. A small red bump will appear at the site if you are allergic to that particular food. For the RAST, a sample of your blood is taken and sent to a laboratory for analysis to determine whether your body has formed antibodies to the food in question. Your doctor also may ask you to record every- thing you eat in a food diary for a couple of weeks to help in the diagnosis.
Many people will outgrow food allergies, except allergies to nuts, ﬁsh, and shellﬁsh. The best treatment for a food allergy is to avoid eating the food that causes the allergic reaction. You will need to read food labels carefully and ask questions when dining out to make sure that the foods you eat do not contain the allergen. Severe allergic reactions are life-threatening. If you have had a previous severe allergic reaction, you will need to carry an injecting device that contains epinephrine with you at all times, so you can inject yourself immediately if you have another allergic reaction.
Warning Signs of Food Allergy
If you have a food allergy, your immune system mistakenly regards a particular food as harmful and begins producing antibodies to that food. Each time you eat that food, your immune system releases various chemicals to protect your body. These chemicals produce symptoms that can affect your airways, skin, or intestinal tract. Symptoms of food allergy can include:
• skin reactions such as hives or rashes
• nasal congestion
• nausea, diarrhea, or gas
• shortness of breath, or asthma attacks in people who have asthma
If the reaction is severe, you may experience life-threatening symptoms within min- utes of eating. A severe allergic reaction can rapidly cause difﬁculty breathing, lowered blood pressure, and loss of consciousness (see “Anaphylactic Shock,” page 383). If you or a person you are with has these symptoms, seek emergency medical help immediately.
The Common Cold and the Flu
The common cold and the ﬂu (inﬂuenza) are both caused by viruses. The viruses that cause colds and the ﬂu are transmitted when an infected person coughs or sneezes into the air and another person inhales the infected droplets. You can also catch a cold or the ﬂu by kissing an infected person or by touching your mouth after touching the other person’s hands or an object he or she has touched. Each cold is caused by a different virus, and there are nearly 200 different cold
viruses. Adults average about two to four colds per year. The virus that causes the ﬂu changes from year to year; that is why a ﬂu immunization is good for only a year. When these viruses enter your body, they multiply rapidly. Your immune system tries to ﬁght them, producing symptoms that include coughing, sneez- ing, and a runny nose.
The ﬂu is a viral infection of the nose, throat, and lungs. It is usually mild in young and middle-aged adults but can be life-threatening in older people and people who have a chronic illness such as heart disease, emphysema, asthma, bronchitis, kidney disease, or diabetes. The ﬂu also can lead to more serious, potentially life-threatening infections such as pneumonia (see page 250). Because pneumonia is one of the ﬁve leading causes of death among older peo- ple, it is important for older people to take steps to prevent the ﬂu. The best pre- ventive measure is a ﬂu shot (see page 93), given each fall at the beginning of the ﬂu season. A pneumonia shot (see page 252) is another preventive measure available for older people and people who have a chronic illness; the pneumonia shot is given only once.
Many people confuse the common cold with the ﬂu, but there is one easy way to tell the difference: the ﬂu usually causes a fever, while a cold does not. Also, a cold causes nasal congestion more often than the ﬂu. In general, cold symp- toms are milder than ﬂu symptoms and do not last as long.
The ﬂu is very contagious. Symptoms differ from person to person, but com- mon symptoms include weakness, body ache, headache, and sudden fever. The fever can last from 1 to 6 days. People with the ﬂu also have a cough, chills, and reddened, watery eyes. If the ﬂu progresses to pneumonia, symptoms become more severe, and chest pain may occur as the lungs become inﬂamed. If the pneumonia was caused by a bacterial infection, it can be treated with antibiotics. Antibiotics are not effective for treating viral infections, including the common cold.
There is no cure for the common cold, and many of the over-the-counter reme- dies available at your local pharmacy (such as pain relievers and decongestants) treat only the symptoms of a cold. Most colds will clear up within a week or so. The usual treatment for the ﬂu is to take aspirin, acetaminophen, or ibuprofen to reduce the fever and body aches, drink plenty of liquids, and rest in bed until after the fever has been gone for 1 to 2 days. Antiviral medications such as amantadine, rimantadine, zanamivir, and oseltamivir are available by prescrip- tion to prevent and treat many types of inﬂuenza.