Effect of ritodrine and betamethasone on metabolism, respiration, and circulation

In order to obtain information on pharmacologic side effects of the most commonly used betamimetic in obstetrics, ritodrine (R) was infused under standardized, controlled conditions in one male and four nonpregnant female volunteers in increasing doses from 0.9 to 7.2 micrograms/kg/min. In second series, the same was done after premedication with 12 mg betamethasone (B), intravenously, 30 minutes before the start of the R infusion. Ritodrine caused increases in cardiac and respiratory work that were associated with rises in energy requirements and impaired efficiency of breathing. Premedication with betamethasone potentiated all side effects with the exception of diffusion capacity.