Evaluation of drugs for arrest of premature labor in a new animal model.

Reported are pharmacologic data from a new animal model used for evaluating drugs from several therapeutic classes for their potential use in the treatment of premature labor. This model measures the spontaneous delivery time between the first and second rat pups in a term pregnancy. In control animals, this averaged 16.3 +/- 4.2 minutes. Ethanol (3.5 gm/kg) and the beta-agonists ritodrine (12.5 mg/kg) and albuterol (0.25 mg/kg) significantly delayed delivery of the second pup. The calcium blockers nifedipine, verapamil, and diltiazem were the most active of all compounds tested in this model. The nonsteroidal anti-inflammatory agents indomethacin and naproxen were inactive at doses as high as 5 and 25 mg/kg, respectively. Metiamide, an H2-antagonist, and dimenhydrinate, an H1-antagonist, were inactive.