[Clenbuterol and fenoterol--animal experiment comparison of 2 tocolytic agents (with special reference to...

During animal experiments two substances, which are used for tocolysis (Fenoterol and Clenbuterol) have been compared regarding their tocolytic efficiency (determinations of myometrial cyclic AMP after long term treatment of the pregnant rat), their effects upon myocardial high energy phosphates (determinations of maternal myocardial high energy phosphates as well as of maternal and fetal myocardial cyclic AMP after long term treatment of the pregnant rat) and upon the hemodynamic situation (acute experiments with thoracotomized dogs). While significant hemodynamic derangements could be stated when using Fenoterol, no significant evidence for such alterations could be found during Clenbuterol administration during acute experiments. Determinations of myocardial high energy phosphates however reflected an augmented myocardial workload, both after Fenoterol and Clenbuterol administration. As by means of myometrial cyclic AMP determinations Clenbuterol proved to be at least as efficient as Fenoterol, concerning the tocolytic effect, Clenbuterol can be recommended as an oral tocolytic because of its pharmaco-cinetic advantages and the encouraging results from our hemodynamic investigations. According to results from chronical experiments an additional cardioprotection by means of magnesium substitution and eventually beta 1-blockade is still recommended.