Table 1.

Food and Drug Administration use-in-pregnancy ratings

A	Controlled studies show no risk	Adequate, well-controlled studies in pregnant women have failed to demonstrate risk to the fetus
B	No evidence of risk in humans	Either animal findings show risk but human findings do not or, if no adequate human studies have been performed, animal findings are negative
C	Risk cannot be ruled out	Human studies are lacking, and results of animal studies are either positive for fetal risk or lacking as well. However, potential benefits may justify the potential risk
D	Positive evidence of risk	Investigational or post-marketing data show risk to the fetus. Nevertheless, potential benefits may outweigh the potential risk
X	Contraindicated in pregnancy	Studies in animals or humans, or investigational or post-marketing reports, have shown fetal risk that clearly outweighs any possible benefit to the patient