IN-VITRO COMPARISON OF 4 TOCOLYTIC AGENTS, ALONE AND IN COMBINATION

Objective: To compare the tocolytic effects of magnesium sulfate, rito drine, terbutaline, and nifedipine on human myometrial strips. Methods : Myometrial strips were suspended in organ chambers for isotonic meas urements and contracted with KCl. Strips from nonpregnant patients wer e used to obtain concentration-response curves. Myometrial strips from pregnant uteri were then exposed to the molar concentrations causing 50% relaxation in the nonpregnant tissues. Results: In strips from non pregnant patients, nifedipine was found to be the most potent tocolyti c. Using strips from nonlaboring patients, nifedipine caused relaxatio n similar to ritodrine, and both were more effective than magnesium su lfate or terbutaline. Combinations were more effective than single age nts. These agents were found to be equally less effective in myometria l strips from laboring patients. Conclusions: Nifedipine, alone or in combination, relaxes myometrial strips more effectively than the other agents studied. Myometrial strips from laboring patients are more res istant to inhibition, with none of the agents being superior.