Pre-Term Labor (prior to 37 weeks gestation) is the largest single cause of infant morbidity and mortality and is frequently associated with long-term disability. Oxytocin is a hormone produced by the body during labor. GSK221149A is an experimental drug that will be used to block the effects of oxytocin, and therefore pause or prevent contractions. In this study, patients with preterm labor will be given an intravenous infusion of GSK221149A over approximately 12 hours followed by an oral tablet in Parts A and B. In part C of this study, patients with preterm labor will be give an intravenous infusion of GSK221149A over approximately 48 hours. The use of a rescue tocolytic is allowed in the study.