Drug use during pregnancy and breast-feeding. A classification system for drug information.

Since 1978 the Swedish catalogue of registered pharmaceutical specialties (FASS) has carried a special section entitled "Pregnancy and breast-feeding" in each product presentation, intended to form an aid for the prescription of drugs to women during childbearing and lactation. After a brief review of transplacental transport and milk secretion, reproduction-toxicology studies in animals, and methods for clinical evaluation of drugs for use during pregnancy, the classification system is presented. On the basis of available data with regard to effects on early and late stages of pregnancy and labour, all the pharmaceutical specialties concerned are assigned to one of the following pregnancy categories: A, B 1, B 2, B 3, C or D. The letters refer to information based on findings in man, and the figures to information based on animal data. For drugs in categories B 3, C or D any harmful effects observed or likely to occur in man or animals are to be specified. The pregnancy categories are defined as follows: Category A. Drugs which may be assumed to have been used by a large number of pregnant women and women of child-bearing age, without any form of definite disturbance in the reproductive process having been noted so far, e.g. an increased incidence of malformations or other direct or indirect harmful effects on the fetus. Category B. Drugs which may be assumed to have been used by only a limited number of pregnant women and women of child-bearing age, without any form of definite disturbance in the reproduction process having been noted so far, e.g. an increased incidence of malformations or other direct or indirect harmful effects on the fetus. Category C. Drugs which by their pharmacological effects have caused, or must be suspected of causing disturbances in the reproduction process that may involve risk to the fetus without being directly teratogenic. Category D. Drugs which have caused an increased incidence of fetal malformations or other permanent damage in man or which on the basis of e.g. reproduction-toxicology studies must be suspected of doing so. This category comprises drugs with primary teratogenic effects. If the drug also has pharmacological effects that may directly or indirectly have a harmful effect on the fetus, this must also be stated. As experience of effects of drugs in Category B is limited, results of reproduction-toxicology studies in animals are indicated by allocation to one of three subgroups according to the following definitions: Category B 1.(ABSTRACT TRUNCATED AT 400 WORDS)