Clenbuterol--a long term uterine relaxant.

Clenbuterol (C.) is a bronchospasmolytic agent which selectively stimulates beta 2-receptors; side-effects of the drug are virtually minimal. C. effects a strong uterine relaxation. The renal elimination after oral administration is 34 hours. In a pilot study 26 women during labor received C. because of uterine hypermotility and increased fetal risk. After oral doses of 40 microgram, 60 microgram and 100 microgram a marked uterine relaxation was achieved in 20 women. Six women did not respond, because the dilatation of the uterine orifice was too much progressed. The effect of an intravenous injection was not superior to that of an oral administration. 21 women with signs of imminent premature birth received C. orally during pregnancy. There were a number of high risk cases among these women. In average a period of uterine relaxation of 63 days was achieved. 18 women reached the 38th week of pregnancy. No cardiovascular side effects were noted in the fetuses, only at the begin of the treatment the mothers showed mild transient palpitations or also transient tremor.