Influence of the beta-1 selective blocker, metoprolol, on the development of pulmonary edema in tocolytic therapy.

Research on one group of nine anesthetized dogs pretreated with alpha-naphthyl-thiourea showed that doses of the beta-sympathicomimetic fenoterol such as those normally administered in clinical tocolysis (2 micrograms/kg per minute) lead to significant fluid displacement to the extravascular space of the lung in the sense of a preclinical interstitial edema. In a second group (N = 9) with the same pretreatment the addition of the beta-1 selective blocker, metoprolol (1.5 micrograms/kg per minute) served to antagonize the hemodynamic changes and possibly the increase of pulmonary capillary permeability induced by the beta-mimetic. Fluid displacement into the interstitium of the lung was prevented by metoprolol. These observations corroborate the hypothesis that pulmonary edema occurring during tocolytic therapy is largely a result of the use of beta-mimetics. In addition to its cardioprotective effect, the administration of the beta-1 selective blocker, metoprolol, may reduce the risk of the development of pulmonary edema in beta-sympathicomimetic therapy for premature labor.