Uterine and cardiovascular effects of aminophylline

Aminophylline (250 mg., over five minutes) was infused intravenously to 10 patients with oxytocin-induced contractions. The uterine activity decreased to 87 per cent because of the effect on contraction intensity; contraction frequency was unaffected. The maximum maternal pulse rate increased to 33 beats per minute. Blood pressure was unaffected. The fetal heart rate and beat-to-beat variability increased. An increased dosage of aminophylline produced unacceptably high maternal tachycardia. Comparing the results to those produced by the beta-sympathomimetic drugs in the same experimental model, it is concluded that aminophylline exhibits poor uterine selectivity with an unfavorable cardiovascular/tocolytic ratio.