In the first half of this year, reports about the adverse reactions of Astemizole (trade name Bismuth) leading to arrhythmia and cardiac arrest were speculated in major media, causing people to be highly concerned about antihistamines. So, what are antihistamines? At present, the drugs used in the treatment of allergic skin disease is mainly antihistamines, antihistamines are divided into H1 receptor antagonists (customarily called antihistamines) and H2 receptor antagonists, in the clinical H1 receptor antagonists are most widely used, dermatologists according to whether the adverse effects of sedation, drowsiness and the application of the time of the sequence of H1 receptor antagonists into two generations. The first generation of antihistamines commonly used are paracetamol (also known as chlorpheniramine), doxorubicin, cyproheptadine, benadryl, anterol (hydroxyzine), dechloroxazine, promethazine (also known as fenugreek), brain Yizine and other drugs; the second generation of antihistamines commonly used are loratadine (keratan), cetirizine (Settsan), imipramine (Petrastine), ibastine (Kestin), astemizole, terfenadine (Mindi) The first generation of antihistamines are known for their ability to be used in a variety of ways. Because the first generation of antihistamines have obvious drowsiness, sedation and other adverse reactions, affecting people’s daily life and study and work, has become increasingly unsuitable for the modern fast-paced life, while most of the second generation of antihistamines have a longer half-life and longer duration of action, can be maintained for 24 hours, only need to be taken orally once a day, rapid absorption, the drug is more difficult to cross the blood-brain barrier, less impact on the central nervous system, does not produce The drug has less effect on the central nervous system, does not produce or has only a slight drowsiness, and has less effect on people’s daily life and study and work, so it is widely welcomed by both doctors and patients, and is most widely used in the clinical application of dermatology, especially for some drivers, high-altitude workers and other special personnel and chronic cases. Clinical studies have shown that the use of this class of drugs in the treatment of urticaria can effectively prevent the occurrence of wind clusters and control itching by taking only one tablet once a day. However, some second-generation antihistamines have certain cardiotoxic effects, and their main cardiotoxic manifestations are: prolongation of QT interval, tip-twist arrhythmia, ventricular tachycardia, supraventricular tachycardia, cardiac arrest and other different types of arrhythmias, and in severe cases, sudden cardiac death. In particular, terfenadine and astemizole have been reported most frequently, in addition to side effects such as dry mouth, fatigue, agitation, gastrointestinal discomfort, headache, hypotension, anxiety, depression, white blood cell count, blood glucose and electrolyte abnormalities. Mild sleepiness, drowsiness, and vertigo can occur with some drugs. Currently, the use of terfenadine has been discontinued in some Western countries, and the U.S. Food and Drug Administration (FDA) classifies terfenadine and astemizole as Class C drugs (less safe class). The vast majority of antihistamine cardiotoxicity is associated with improper dosing, blind dose increases, coexisting cardiac disorders, and electrolyte disturbances. Since the 1990s, syncope and tip-twisting ventricular tachycardia have been reported worldwide with specific second-generation antihistamines (terfenadine, astemizole). From 1986 to 1996, the World Health Organization (WHO) analyzed the side effects of second-generation antihistamines in 17 countries and found that 98 cases of terfenadine caused sudden cardiac death, 864 cases caused different types of arrhythmias, and 429 cases caused specific cardiac complications when applied; 25 cases of astemizole caused sudden cardiac death, 233 cases caused different types of arrhythmias, and 110 cases caused specific cardiac complications; and 25 cases of astemizole caused sudden cardiac death, 233 cases caused different types of arrhythmias, and 110 cases caused specific cardiac complications. (The cardiac toxicity of loratadine is rarely reported in the domestic literature, but according to the author’s clinical experience, the drug is safe and drowsiness is very rare); cetirizine has 2 cases of sudden cardiac death, 15 cases of special cardiac complications, and 19 cases of the above-mentioned complications. complications, and 19 cases of the above-mentioned arrhythmias. In view of the cardiotoxicity of second-generation antihistamines, it is particularly important to use second-generation antihistamines rationally to avoid the occurrence of cardiotoxicity. Therefore, when clinicians use these drugs, they should keep in mind the following precautions: 1. It is prohibited to use them together with macrolide antibiotics (such as erythromycin, azithromycin, roxithromycin, clarithromycin) and azole antifungals (such as ketoconazole, itraconazole, fluconazole), otherwise they may cause an increase in the blood concentration of second-generation antihistamines, resulting in ventricular arrhythmias and even sudden cardiac death. There are more than 100 cases of sudden cardiac death caused by the simultaneous use of Astemizole and Teflutinin with erythromycin or ketoconazole, and these drugs are widely used in clinical practice, so it is worthwhile for clinicians to pay high attention to them. 2, patients with heart disease avoid use. These diseases themselves can have prolonged QT intervals and form various arrhythmias, and the application of second-generation antihistamines increases the risk of arrhythmia induced by this class of drugs. 3, electrolyte disorders (such as hypokalemia, hypocalcemia, hypomagnesemia, etc.) to avoid the use of electrolyte disorders can affect the depolarization of the ventricular muscle, resulting in the prolongation of the QT interval on the electrocardiogram. 4.Avoid the use with anti-arrhythmic drugs (such as quinidine, clonidine), calcium antagonists such as (Prilamine), sedative-hypnotics (such as chloral hydrate), etc. 5, try not to exceed the recommended dose of this type of drugs, the more serious cases can be combined with the application of different types of antihistamines to improve the efficacy, in order to prevent the occurrence of drug resistance phenomenon, antihistamines can be used alternately. 6. When working at height, drivers and machine operators have to use antihistamines, they should use loratadine and desloratadine, and should take them orally at night and suspend their work when necessary. 7, children over 2 years old can use loratadine, desloratadine, cetirizine, levocetirizine; children under 12 years old should use imipramine, ibastine and other drugs with caution. 8. Second-generation antihistamines are prohibited for pregnant and lactating women. 9, Prostate hypertrophy, pyloric obstruction patients are cautioned to use methaqualazine. 10, Imipramine is generally not taken at the same time with cimetidine, cyclosporine, cardiac pain. With the exposure of cardiotoxicity of Xithromax by major media, many patients have doubts about the use of second-generation antihistamines, but in fact, the side effects of antihistamines are very few compared with antibiotics and hormones. This indicates that the use of second-generation antihistamines is still relatively safe under the premise that dermatologists strictly control the application of the drugs. Xithromax was the first second-generation antihistamine without drowsiness to be used in clinical practice (marketed in 1988). At that time, Xi’an Janssen invested a lot of money in advertising the drug, making it a household name and widely used. As the saying goes, “a drug is poisonous in three parts”, we must not choke on the cardiotoxic effects of second-generation antihistamines, and patients can safely use second-generation antihistamines as long as they are under the guidance of dermatologists.