Ans: B > A (Nifedipine > Ritodrine)Ref: DC Dutta's Textbook of Obstetrics, pg: 508Explanation:Best answer would be b) Nifedipine (Most likely) > a) Ritodrine (as there is no clear first-line tocolytic agent).Common Tocolytic Agents, Their Mechanism and Side Effects DrugMechanismDescriptionPossiblecontraindicationsMaternal side effectsFetal and neonatal side effectsTerbutalineb2-agonistIs often the drug given first, especially if there is only low risk of preterm birthCardiac arrhythmias diabetes* Cardiac arrhythmias* Cardiopulmon ary diseases* Pulmonary- edema* Myocardial ischemia* Hypertension* Tachycardia* Fetal tachycardia* Hyperinsulinemia* Hypoglycemia* Myocardial and septal hypertrophy* Myocardial ischemiaRitodrineb2-agonistNo longer had FDA approvedPoorly controlled thyroid disease and diabetesMetabolic hyperglycemia* Hyperinsulinemia* Hypokalemia* Antidiuresis* Altered thyroid function* Physiologic tremor* Palpitations* Nervousness* Nausea or vomiting* Fever* Hallucinations* Neonatal tachycardia* Hypoglycemia* Hypocalcemia* Hyperbilirubinemia* Hypotension* Intraventricular hemorrhageNifedipineCCBsIs one of the most commonly used tocolytic agentsCardiac disease It should not be used concomitantly with magnesium sulfate* Flushing* Headache* Dizziness* Nausea* Transient hypotension.* Renal disease and hypotension.* Concomitant use of calcium channel blockers and magnesium sulfate may result in cardiovascular collapse* None noted as yetAtosibanOxytocinantagonistless side effects than 62 recep agonist IndomethacinNSAIDs Late pregnancy (ductus arteriosus}, significant renal or hepathic Impairment* Nausea* Heartburn* Constriction of ductus arteriosus* Pulmonary hypertension* Reversibe decrease in renal (unction with oligohydramnios* intraventricular hemorrhage* Hyperbilirubinemia* Necrotizing enterocolitisSulindacNSAIDs Coagulation disorders or thrombocytopenia, nonsteroidal anti-inflammatory drug (MSAID)-sensitive asthma, other sensitivity to NSAIDs IVMagnesiumsulfateMyosin lightchaininhibitorShewn to be ineffective.Has been recommended for women at high risk. However, meta-analyses have failed to support it as a tocolytic agent.AbsolutecontraindicationMyasthenia gravis* Flushing* Lethargy* Headache * Muscle weakness* Diplopia* Dry mouth* Pulmonary edema* Cardiac arrest* Lethargy* Hypotonia* Respiratory depression* Derrl penalization with prolonged useCalcium-channel blockers and an oxytocin antagonist can delay delivery by 2.7 days. Otherwise tocolysis is rarely successful beyond 24-48 hours because current medications do not alter the fundamentals of labor activation.However, just gaining 48 hours is sufficient to allow the pregnant women to be transferred to a center specialized for management of preterm deliveries and administer corticosteroids to reduce the possibility of neonatal organ immaturity.Contraindications to TocolysisGestational age > 34 weeks gestation.Intrauterine Growth Restriction (IUGR) or placental insufficiency.Lethal congenital or chromosomal abnormalities.Cervical dilation > 4 cm.Chorioamnionitis or intrauterine infection.Fetal distress or fetal death.Mother has severe pregnancy-induced hypertension.Eclampsia/preeclampsia.Active vaginal bleeding.Placental abruption.Cardiac disease.