1, Overview FDA is the abbreviation of the U.S. Food and Drug Administration, established in 1927, first known as the Food, Drug and Pesticide Administration, renamed the Food and Drug Administration in 1930. The U.S. federal government authorized the FDA to be responsible for the management and monitoring of imported food, drugs and health products. The agency classifies the safety of drugs into five categories A , B , C , D , X according to the different degrees of teratogenic risk to animals or pregnant women. Some drugs have two different danger levels, one is the level of common dose and the other is the level of extraordinary dose. The five FDA classification criteria are described below. Classification A: No risk to the fetus has been shown in women with early pregnancies with controls (and no evidence of risk in mid- and late-term pregnancies), and the potential harm to the fetus is minimal. Category B: No risk to the fetus in animal reproduction tests without maternal controls, or with side effects (less severe than sterility) in animal reproduction tests, but no certainty of side effects in controls of early pregnant women (and no evidence of risk in mid- and late-term pregnancies). Classification C: Fetal side effects (teratogenic or embryonic lethal or otherwise) have been demonstrated in animal studies, but there are no controls in women or no available information in women and animal studies. Drugs are given only when the balance of benefits to the fetus outweighs the harms. Category D: A drug with positive evidence of risk to the human fetus, but which, although harmful, requires a positive benefit to the pregnant woman before it is given (e.g., for life-threatening or serious illness where safer drugs cannot be applied or where the drug is ineffective). Classification X: A drug that has been shown to cause fetal abnormalities in animal or human studies or is known to be dangerous to the fetus based on human experience, harmful to humans or to both, and whose use in pregnant women clearly outweighs any beneficial effects. The drug is contraindicated in women who are pregnant or will become pregnant. 2, a brief introduction to each classification of drugs Classification A class: Classification A class of drugs are very few, vitamins belong to such drugs, such as a variety of vitamin B, C, etc., but in the normal range of doses of vitamin A is a class A drug, while large doses of vitamin A, a daily dose of 20,000 IU, can be teratogenic, and become a class X drug. Class B: There are not many drugs in Class B. Happily, all daily antibiotics are in this category. For example, all penicillins and most cephalosporins are class B drugs, and commonly used ampicillin, cefradine, ceftazidime and ceftazidime used for resuscitation in severe infections are all class B drugs. In addition, jelamycin, clofibrate, erythromycin and furantoin are also class B drugs. Here, it is necessary to make some introduction to metronidazole, which is known to be a drug for trichomoniasis, but it is also an excellent drug for anaerobic bacterial infections. Although it can be teratogenic in rodents in animal studies, in humans, a large amount of clinical data accumulated over a long period of time has confirmed that its application in early pregnancy does not increase the teratogenicity of the fetus. Therefore, metronidazole is classified as Class B in the FDA pregnancy drug classification. Among the anti-tuberculosis drugs, ethambutol is a class B drug. However, it should be noted that after 32 weeks of gestation, indomethacin may cause fetal arterial stenosis or atresia, resulting in fetal death. 32 weeks later, indomethacin should not be taken. Among the cardiovascular system drugs, digitalis, digoxin, and cetirizine are all class B drugs. Among the adrenocorticotropic hormones that are harmful to the fetus, prednisone is also a class B drug. Class C: There are more drugs in Class C. These drugs have either not been introduced for a long time or are rarely used in pregnant women, and it is difficult to draw a definite conclusion as there are no reports on whether they can cause damage to the fetus mainly in early pregnancy. Take the antibiotic quinolones as an example, this class of drugs in animal experiments found oxyfloxacin damage to cartilage, in humans there are reports of more than 6 0 0 cases of early pregnancy taking the drug, after the delivery of children in the growth period of 6 cases have leg pain, but soon after the symptoms disappeared, none of the sequelae, so the argument of the data, the drug is still safe. However, the clinic still has to wait for more reports to confirm its harmlessness. Caution should be exercised in the use of Class C drugs. If an alternative drug is available, choose the alternative drug; otherwise, after weighing the pros and cons, explain to the patient or the patient’s family the reasons for choosing the drug. In the case of tuberculosis, for example: since only one of the commonly used anti-tuberculosis drugs is ethambutol, a class B drug, and anti-tuberculosis treatment is often a combination of several drugs, it is necessary to consider the application of class C drugs such as sodium para-aminosalicylate and isoniazid, etc. If the patient is in early pregnancy and has combined tuberculosis, the patient should be informed of the situation. Antiviral drugs, most of which belong to class C, such as acyclovir, i.e. acyclovir and zidovudine for AIDS disease. Some antiepileptic drugs and sedatives such as ethosuximide , nonaminobarbitone, pentobarbitone, etc. Among the autonomic nervous system drugs, cholinergic and anticholinergic drugs belong to class C. Some of the adrenergic drugs belong to class C, such as epinephrine, ephedrine, dopamine, etc. Among the antihypertensive drugs, methyldopa, prazosin and all commonly used vasodilators, such as phenazopyridine, alazoline and pentoxifylline, are in class C. Among the diuretics, furosemide (tachyphylaxis) and mannitol are all class C drugs. Among the adrenocorticosteroids, betamethasone and dexamethasone are all Class C drugs. Class D: Because of the available experimental and clinical evidence, drugs classified as Class D are not used during pregnancy, especially in the early stages of pregnancy, if possible. Among antibiotics the tetracycline family is a typical one. The use of tetracycline or hygromycin during pregnancy destroys the fetal tooth enamel and results in yellowing of the teeth by the time of adulthood, which is a consequence of the use of tetracyclines. Aminoglycosides are not used during pregnancy as much as possible, such as streptomycin, which may damage the eighth pair of cranial nerves and cause hearing loss. As for antineoplastic drugs, almost all of them are class D drugs, taking methotrexate (MTX) as an example, in the late 1940s, it was recognized that the application of MTX in leukemia combined with pregnancy could lead to miscarriage due to chorionic villous necrosis, so in the early 1950s, Hertz et al. developed the idea of treating choriocarcinoma with MTX and achieved success. Today, MTX is widely used to treat trophoblast-related diseases, such as ectopic pregnancy and placental implantation; other antineoplastic drugs such as cisplatin and 5-fluorouracil have also joined the ranks. Therefore, antineoplastic drugs are contraindicated during pregnancy. Analgesics in the central nervous system drugs, used in small doses as class B drugs, and in large doses as class D drugs, especially long-term application is harmful to the fetus, mainly manifested by poor fetal growth and development and addiction to drugs after delivery, irritability, crying, etc. The fetal malformation rate of fetuses of patients with epilepsy after pregnancy is higher than that of the general population. This is something that must be clearly explained to the patient and family when treating pregnancy with epilepsy. Among the sedative and hypnotic drugs, diazepam (Valium), chlordiazepoxide (Librium), meprobamate (Meprobamate) and norethindrone are all class D drugs. Among diuretics, hydrochlorothiazide, etanercept and benserazide are all class D drugs and should not be used during pregnancy. As for the antipyretic and analgesic drugs, aspirin, bisalicylic acid and sodium salicylate are Class C drugs when used in small doses, but when taken in large doses for a long time, sometimes even addictive, they are unfavorable to the fetus and become Class D drugs. In fact, there are thousands of drugs available for people to apply, and there are B, C and D drugs in all kinds of drugs, so people can choose B drugs or C drugs instead of D drugs. Class X: There are not many of these drugs in common use, but they are prohibited during preconception and pregnancy because of their high teratogenic rate or danger to the fetus. In the late 1950s and early 1960s, women in the vicinity of the Allied stations in Europe took this drug in the early stages of pregnancy to reduce pregnancy reactions, and later found that many fetuses were born with short upper limbs and combined lower limbs in the shape of seals. In the early 1950s, the sex hormone oestradiol was used to treat pre-eclampsia, but it was found that vaginal adenopathy or vaginal clear cell carcinoma could occur in women between the ages of 6 and 26, and the consequences were serious. These are two famous cases in drug teratogenesis. Vitamin A can also be teratogenic when taken orally in large doses and is also a class X drug. Vitamin A derivative, retinoic acid, is a drug for skin diseases and is also a class X drug. However, what is often overlooked is heavy alcohol consumption, such as heavy alcohol consumption in early pregnancy, and intake of large amounts of ethanol, 150 ml or more per day can cause fetal dysplasia or developmental malformations. Therefore, ethanol in the FDA classification of alcohol consumption in small amounts belong to category D, the amount of more that is classified as X category. In addition, among the sedative drugs, flurazepam (fluorazepam) and flunitrazepam (flunitrazepam) are in category X. The antineoplastic drug aminopterin is also in category X.