4. Donor must not be pregnant or breastfeeding an infant. A donor who is lactating must substitute formula feeding for her infant during the period of cytokine administration. Filgrastim may be secreted in human milk, although its bioavailability from this source is not known. Limited clinical data suggest that short-term administration of filgrastim or sargramostim to neonates is not associated with adverse outcomes. Donors of childbearing potential must use an effective method of contraception during the time they are receiving cytokines. The effects of cytokine administration on a fetus are unknown and may be potentially harmful. The effects upon breast milk are also unknown and may potentially be harmful to the infant.