Betamethasone dose and formulation for induced lung maturation in fetal sheep.

We hypothesized that maternal treatments with betamethasone acetate induce fetal lung maturation comparably to the betamethasone phosphate+betamethasone acetate used clinically. Ewes with singleton pregnancies were treated with single doses of 0.25-mg/kg or 0.5-mg/kg betamethasone acetate, 4 doses of 0.25-mg/kg betamethasone phosphate, a single dose of 0.5-mg/kg betamethasone acetate+0.25-mg/kg betamethasone phosphate, 2 doses of 0.25-mg/kg betamethasone acetate+0.25-mg betamethasone phosphate or vehicle beginning 48 hours before preterm delivery. Fetal lung maturation was evaluated. All treatments induced lung maturation relative to vehicle controls. The relatively insoluble betamethasone acetate resulted in low maternal blood betamethasone and no detectable fetal blood betamethasone in 2 of 3 fetuses, but it induced fetal lung maturation comparable to the 2-dose betamethasone acetate+betamethasone phosphate or 4 doses of betamethasone phosphate. A single maternal dose of betamethasone acetate effectively induces fetal lung maturation in sheep with minimal fetal exposure.