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In vitro comparison of four tocolytic agents, alone and in combination
G R Saade1, O Taskin, M A Belfort
1Department of Obstetrics and Gynecology, Baylor College of Medicine, Houston, Texas.
Objective:
To compare the tocolytic effects of magnesium sulfate, ritodrine, terbutaline, and nifedipine on human myometrial strips.
Methods:
Myometrial strips were suspended in organ chambers for isotonic measurements and contracted with KCI. STrips from nonpregnant patients were 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 nonpregnant patients, nifedipine was found to be the most potent tocolytic. Using strips from nonlaboring patients, nifedipine caused relaxation similar to ritodrine, and both were more effective than magnesium sulfate or terbutaline. Combinations were more effective than single agents. These agents were found to be equally less effective in myometrial 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 resistant to inhibition, with none of the agents being superior.
Insights
Nifedipine demonstrated superior tocolytic effects on human myometrial strips compared to magnesium sulfate, ritodrine, and terbutaline. However, myometrial strips from laboring patients showed resistance to all tested tocolytic agents.
Area of Science:
- Obstetrics and Gynecology
- Pharmacology
- Reproductive Medicine
Background:
- Preterm labor is a significant concern in obstetrics.
- Tocolytic agents are used to inhibit uterine contractions.
- Comparing the efficacy of different tocolytic drugs is crucial for clinical practice.
Purpose of the Study:
- To compare the tocolytic efficacy of magnesium sulfate, ritodrine, terbutaline, and nifedipine.
- To evaluate these agents on human myometrial strips.
- To assess potential differences in efficacy between nonpregnant, nonlaboring, and laboring myometrial tissues.
Main Methods:
- Human myometrial strips were used for isotonic measurements in organ chambers.
- Concentration-response curves were generated using KCI contractions in nonpregnant tissues.
- Strips were exposed to molar concentrations that induced 50% relaxation in nonpregnant tissues.
Main Results:
- Nifedipine exhibited the most potent tocolytic effect in nonpregnant tissues.
- In nonlaboring pregnant tissues, nifedipine and ritodrine showed similar efficacy, superior to magnesium sulfate and terbutaline.
- Combinations of agents were more effective than single agents in nonlaboring tissues.
- All agents were less effective in myometrial strips from laboring patients.
Conclusions:
- Nifedipine, alone or in combination, is more effective in relaxing myometrial strips than the other agents studied.
- Myometrial strips from laboring patients are more resistant to tocolytic inhibition.
- No single agent demonstrated superiority in inhibiting contractions from laboring myometrial tissues.