In the first half of this year, reports about the adverse reactions of Astemizole (trade name Bismuth) causing arrhythmias 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 diseases are 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 effects 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, co-morbid cardiac disorders, and electrolyte disturbances. Since the 1990s, a number of specific second-generation antihistamines (terfenadine, astemizole) have been reported worldwide to cause syncope and tip-twisting ventricular tachycardia, and side effects of second-generation antihistamines were analyzed by the World Health Organization (WHO) in 17 countries from 1986 to 1996, and found that 98 cases of terfenadine were associated with In the analysis of the side effects of second-generation antihistamines in 17 countries, it was found that 98 cases of terfenadine caused sudden cardiac death, 864 cases caused different types of arrhythmias, and 429 cases caused specific cardiac complications; 25 cases of astemizole caused sudden cardiac death, 233 cases caused different types of arrhythmias, and 110 cases caused specific cardiac complications; 13 cases of loratadine caused sudden cardiac death, 106 patients caused specific cardiac complications, and 286 cases caused different types of arrhythmias. According to the author’s clinical experience, this drug has a high safety profile and drowsiness is very rare); cetirizine had 2 cases of sudden cardiac death, 15 cases of specific cardiac 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 must 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 administration of Astemizole and Teflutinin with erythromycin or ketoconazole, and the above-mentioned drugs are widely used in clinical practice, so it is worthwhile for clinicians to pay high attention to them. 2. These diseases themselves can appear QT interval prolongation, the formation of various arrhythmias, the application of second-generation antihistamines, will increase the risk of arrhythmia induced by this type of drugs. 3, electrolyte disorders (such as hypokalemia, hypocalcemia, hypomagnesemia, etc.) avoid use, electrolyte disorders can affect the depolarization of the ventricular muscle, resulting in the prolongation of the QT interval on the electrocardiogram. 4, avoid the same anti-arrhythmic drugs (such as quinidine The use of antihistamines can be combined with antiarrhythmic drugs (e.g. quinidine, chloroquine), calcium antagonists such as prilamine, sedative-hypnotics (e.g. chloral hydrate), etc. The recommended dose of these drugs should not be exceeded, and in severe cases, different types of antihistamines can be combined to improve the efficacy. The remaining second-generation antihistamines are still sedative and drowsy to varying degrees in some patients. 7. Children over 2 years of age may use loratadine, desloratadine, cetirizine, levocetirizine; children under 12 years of age should use imipramine and epalrestine with caution. 8. Pregnant and lactating women are prohibited from using second-generation antihistamines. 9. Use methaqualazine with caution in patients with prostatic hypertrophy and pyloric obstruction.10. Imipramine is generally not taken concurrently with cimetidine, cyclosporine, and cardiac painkillers. With the exposure of the cardiotoxicity of Xithromax in the media, many patients have doubts about the use of second-generation antihistamines, but in fact, the side effects of antihistamines are rare 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, which made it a household name and was widely used. As the saying goes, “medicine is three parts toxic”, we must not choke on the cardiotoxic reactions of second-generation antihistamines, and patients can use second-generation antihistamines as long as they are under the guidance of dermatologists.