Cardiovascular and metabolic effects associated with nifedipine and ritodrine tocolysis

Recent investigations have indicated that nifedipine, a calcium channel entry blocker, may be useful in the treatment of preterm labor. This prospective, randomized study compares cardiovascular and metabolic effects measured in association with sublingual and oral administration of nifedipine with those noted with the intravenous and oral administration of the beta-adrenergic agent ritodrine. Serial measurements of cardiovascular parameters, hematocrit, electrolytes, glucose, blood urea nitrogen, creatinine, calcium, and serum glutamic-oxaloacetic and glutamic-pyruvic transaminase were compared between groups. Sublingual and oral nifedipine caused minimal cardiovascular alterations. At doses sufficient to achieve tocolysis, ritodrine caused more pronounced cardiovascular changes than nifedipine. Both agents had a hemodilutional effect, but nifedipine was not associated with alterations in serum electrolytes or a dramatic hyperglycemia. On the basis of this study, it appears that the use of nifedipine for preterm labor management is associated with hemodilutional changes but not the adverse cardiovascular or metabolic effects often associated with ritodrine tocolysis.