In clinical practice, many pain patients require medication, and some of these patients can have adverse reactions to medications, including what is often called an allergic reaction, also known as a drug allergic reaction. An allergic reaction is an abnormal immune response. A normal immune response results in resistance to pathogens. By “strengthening immunity”, we mean improving the body’s ability to resist disease-causing microorganisms and abnormal reactions in the body, thereby preventing infectious diseases, maintaining a stable body condition, and monitoring abnormalities (e.g., cancerous changes) occurring in the body and invasive foreign substances (e.g., microorganisms and other foreign proteins) invading from outside of the body to prevent and treat diseases. Therefore, a normal immune response is absolutely essential for the maintenance of life. When normal immunity is severely compromised (e.g., acquired immunodeficiency syndrome, or AIDS), life will not be sustained. Abnormalities in the immune response, whether too strong or too weak, are detrimental to the body and can cause a range of pathologies; such conditions caused by drugs are drug allergies. Causes of Drug Allergy There are two necessary factors for the development of drug allergy: allergy and contact with the drug, both of which are indispensable. Allergies are genetically determined and there is no way to change them. People with genetic allergies make up about 1/3 or more of the population, and these people are prone to allergic diseases such as allergic rhinitis, bronchial asthma, hives, eczema, etc.; another factor is exposure to allergenic drugs. Not all drugs can cause allergic reactions. Drugs that can cause an allergic reaction are called sensitizing drugs. Therefore, drug allergy occurs only in people with allergies and must be caused by medication. Importance of drug allergy and its current status Drug allergy is the earliest category of allergic reactions recognized by mankind. During the Middle Ages in Europe, virulent infectious diseases such as bubonic plague and cholera killed large numbers of people and even destroyed towns and cities. The only effective treatment at that time was to inject the survivors with their recovery serum. While a large number of patients benefited from this treatment, a small number of people suffered severe reactions and even deaths as a result of the serum injections. This was the first human observation of the phenomenon of allergic reactions, and the study of this phenomenon led to the formation of a new discipline – allergology. Drug allergy is a category of adverse drug reactions. Adverse drug reactions include drug poisoning, drug allergy, drug intolerance, drug-drug interactions and so on. People used to be most familiar with drug poisoning. As the saying goes, “medicine has three poisons”, which means that drugs have a dual nature, with both favorable therapeutic aspects and unfavorable toxic reactions. In the early stages of drug therapy, most of the drugs used are natural substances. The therapeutic effect of these drugs is generally poor, and the toxicity is also large. The toxic effects of drugs are generally parallel to the dose. The higher the dose, the greater the toxic reaction, which is an irreconcilable contradiction. When the dose is increased in order to improve the therapeutic effect, the toxicity of the drug also increases accordingly. Therefore, poisoning often occurs in the early stages of drug therapy. With the development of pharmaceutical industry, high efficiency and low toxicity of synthetic drugs gradually replaced natural drugs, thus improving the therapeutic effect. However, many synthetic drugs have strong sensitizing properties, leading to an increased incidence of drug allergy. Drug allergy has become a prominent problem of adverse drug reactions today. Clinical manifestations of drug allergy The clinical manifestations of drug allergy are varied and can belong to any type of allergic reaction, and in many cases, it is the synthesis of multiple types of allergic reactions. 1, drug fever fever caused by drug allergy is called drug fever. It is often the earliest manifestation of drug allergy. Drug fever and general infectious fever is different, it is characterized as follows: if it is the first time to use the drug, fever can be about 10 days after the sensitization period; if it is the second time to use the drug, because the body has been sensitized, fever can occur rapidly. Drug fever occurs again because of the rapid occurrence of drug fever, easy to associate with the use of drugs; and the first use of drugs occurring drug fever due to the long interval, the patient often do not think that the previous use of drugs related to, or can not recall the history of the use of drugs, which makes the diagnosis of a certain degree of difficulty. Drug fever is usually a persistent high fever, often up to 39 ℃, or even more than 40 ℃. But although the fever is high, the patient’s general condition is still good, and the heat is not proportional; the application of a variety of antipyretic measures (such as antipyretic drugs) is not effective; but such as stopping the use of allergy-causing drugs, sometimes even if you do not take anti-allergy measures, the body temperature can also be reduced on its own. 2, drug rash drug allergy can often cause a rash, known as drug rash. Drug rash usually follows the drug fever; but can also occur before the drug fever. Rash can have a variety of forms, such as measles-like, scarlet fever-like, eczema-like, urticaria-like, purpura-like, herpes-like and so on. There is a class of fixed drug rash, which is characterized by a rash caused by the same drug, each attack occurs in the same fixed site. At first, it is red, and then gradually turns into dark brown, which is difficult to subside, or even does not subside for a lifetime. The drugs that cause this kind of rash mainly include phenolphthalein (laxative), barbiturates (sedative), sulfonamides, heavy metal salts (such as bismuth, antimony), arsenic and so on. However, the morphology of most of the drug rash is not specific, that is to say, the drug rash can not be based on the morphology of the drug rash to determine the sensitizing drugs. 3, serum sickness-like reaction Serum sickness is the first application of serum (such as horse serum) preparations, after about 10 days of an allergic reaction. Clinical manifestations are fever, enlarged lymph nodes, arthralgia, hepatosplenomegaly and so on. Serum sickness that occurs due to injection of xenogeneic serum is generally milder in clinical manifestations and is often self-limiting. As the serum level drops, the acute symptoms usually disappear after 3 to 5 days and other symptoms gradually resolve. Due to the introduction of chemotherapeutic agents and antibiotics, the diseases that require the use of serum preparations are now limited to a few. However, non-serum agents can also cause these clinical manifestations by similar mechanisms, especially synthetic drugs. Therefore, these diseases are also called serum sickness or serum sickness-like reaction. 4, other systemic damage Severe allergic drug reactions can cause systemic damage, such as anaphylaxis, blood cell reduction (hemolytic anemia, granulocytopenia, thrombocytopenia, etc.); respiratory symptoms (rhinitis, asthma, alveolitis, pulmonary fibrosis, etc.); digestive symptoms (nausea, vomiting, abdominal pain, diarrhea, etc.); liver damage (jaundice, bile stagnation, hepatic necrosis, etc.); renal damage (hematuria, proteinuria, renal failure, etc.). proteinuria, renal failure, etc.); neurological damage (migraine, epilepsy, encephalitis, etc.). Treatment of drug allergy: 1, immediately stop using all the suspected disease-causing drugs, avoid in the aura of drug reaction has appeared when still not categorically stopping the practice of drugs. 2, to give the patient with favorable conditions, avoid unfavorable factors. Such as bed rest, diet rich in nutrients, maintain a suitable warm and cold environment, prevent secondary infections. 3.Apply camphor or menthol-containing glycerite lotion, oscillating lotion or powder several times a day to relieve itching, dissipate heat and reduce inflammation. 4.Traditional treatment: 1~2 kinds of antihistamine drugs orally. 5.Severe with antibiotics: choose appropriate antibiotics to prevent infection, but must be careful, because patients with severe drug rash, often in a highly allergic state, not only prone to cross-sensitivity to drugs, but also may appear polygenic allergy, that is, allergic to the original sensitizing drugs in the structure of the drug is completely unrelated to the drugs that cause a new drug rash.