- Pregnant women are excluded from this study because gemcitabine is an antimetabolite (pyrimidine analog) with the potential for teratogenic or abortifacient effects. Because there is an unknown but potential risk for adverse events in nursing infants secondary to treatment of the mother with gemcitabine, breastfeeding should be discontinued if the mother is treated with gemcitabine. These potential risks may also apply to other agents used in this study.