Does the administration of the calcium-antagonist verapamil in tocolysis with beta-sympathicomimetics still make sense?
In tocolysis with beta-sympathicomimetics Verapamil is administered universally to reduce the subjective and objective cardiovascular side effects. The efficacy of the calcium-antagonist has not yet been substantiated. This has now re-emerged as an important issue due to the increasing occurrance of cardiopulmonary complications in tocolysis, some fetal. Nine mongrel German shepherds were anesthetized and relaxed, and their breathing was controlled at constant volume. After infusion of Fenoterol (0.06 microgram/kg/min) and subsequent administration of Verapamil (2 microgram/kg/min) a continuous record was made of the parameters of the pulmonary and systemic circulatory systems, the cardiac dynamics, the acid-base balance, the blood gases with O2 absorption and CO2 output, electrolytes and the colloid osmotic pressure. Furthermore, the intrapulmonary fluid volumes in the vascular system and the interstice were measured. During infusion with Fenoterol the changes expected from a beta-adrenergic were observed in the form of a hyperkinetic cardiac situation, metabolic acidosis and increased exchange of gases. Also pronounced fluid shifts in the lungs occurred from the intravascular space to the interstice. Subsequent administration of the calcium antagonist showed no influence on the beta-mimetic-induced changes demonstrated in the present work. The results agree with previous clinical investigations. According to the known dosage curve, the dosage of Verapamil would have to be increased multifold to achieve an effect, which is hardly possible due to the cardiodepression and peripheral circulation drop with hypotension that this would entail. The administration of Verapamil in tocolysis no longer appears expedient.