A primigravida is admitted to the labor and delivery unit complaining of intermittent backache and abdominal cramping. She has had an uncomplicated pregnancy and there is no evidence of ruptured amniotic membranes. Fetal gestational age of 32 weeks correlates with fundal height and date of last menstrual period. The fetal heart rate is 130 to 140. Mild contractions of 30-second duration can be felt every 4 to 5 minutes. A vaginal exam reveals 3 cm dilation, 80 percent effacement, and 0 station. Urinalysis from a sterile catheterized specimen is negative for bacteria and white blood cells. The obstetrician orders an immediate intravenous infusion of ritodrine hydrochloride (Yutopar)-a uterine relaxant. The obstetrical