PHAR 266: LO1- FDA Risk Letter Stratification System

category A

-adequate and well-controlled studies fail to demonstrate risk to fetus in first trimester (or in later trimesters)

category B

-animal studies fail to demonstrate risk to fetus and there are no adequate and well-controlled studies in pregnant women

category C

-animal reproduction studies have shown adverse effect on fetus and there are no adequate and well-controlled studies in humans, but potentially benefits may warrant use of drug in pregnant women despite potential risks

category D

There is positive evidence of human fetal risk based on adverse reaction data from investigational or marketing experience or studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks

category X

Studies in animals or humans have demonstrated fetal abnormalities and/or there is positive evidence of human fetal risk based on adverse reaction data from investigational or marketing experience and the risks involved in use of the drug in pregnant women clearly outweigh potential benefits