Tocolytic agents

Tocolytic agents Medications that can stop labor by slowing down or halting the contractions. 

Ritodrine is a selective Sj-adrenoreceptor stimulant, predominantly of the urino-genital system. It is used as a tocolytic agent for problems associated with premature miscarriages, and only in specialized medical facilities. Synonyms of ritodrine are yutopar and pre-par. 

Samples from cattle, sheep, horse, poultry, and ratite were tested for the -agonists clenbuterol, salbutamol, and cimaterol. Clenbuterol has restricted use and is registered as a tocolytic agent for tire facilitation and postponement of parturition in cattle and sheep and as a bronchodilator and expectorant in horses. 

If labour begins prematurely, before 33 weeks gestation, myometrial relax-ants (tocolytic agents) can delay it for 48 hours. Beta-2-agonists, such as ritodrine hydrochloride, are given for up to 48 hours to elicit relaxation. Longer treatment is not recommended, because of risk of adverse effects on the mother. Nifedipine and the oxytocin receptor antagonist atosiban are also used to reduce premature uterine contractile activity. 

A single case report supports the hypothesis that a COX-2-selective NSAID might have the efficacy of indometacin as a tocolytic agent without its adverse effects in the fetus (148). 

The incidence and type of cerebral lesions were studied by ultrasound in 159 preterm infants 76 fetuses were exposed to indometacin used as a tocolytic agent in the other 83 pregnancies, tocolysis was either not started or limited to fenoterol. The incidence of periventricular leu-komalacia was increased in infants exposed to any tocolytic agent cystic lesions occurred more often in those exposed to indometacin (50). 

Antenatal indometacin therapy has been extensively reviewed (SEDA-18, 102). Data from a retrospective cohort study of 57 premature infants, bom between the 24th and 30th weeks of gestation, whose mothers had been treated unsuccessfully with indometacin for preterm labor, confirmed several fetal and neonatal complications (52). However, the overall results provided inconclusive or contradictory data on the benefit to harm balance of indometacin as a tocolytic agent or as treatment for hydramnios (SEDA-18,102). 

The possible association of indometacin tocolysis with neonatal necrotizing enterocolitis has been the subject of a case-control study (53). All cases of proven necrotizing enterocolitis were ascertained and four controls for each case were randomly identified. During 18 months there were 24 cases of necrotizing enterocolitis. Indometacin as a single tocolytic agent was not associated with necrotizing enterocolitis (OR = 1.0, 95% Cl = 0.2, 4.8). 

A report has confirmed the potential danger of using nimesulide as a tocolytic agent (SEDA 24, 123). Nimesulide (100 mg bd) was prescribed for postoperative preterm labor prophylaxis, and severe oligohydramnios was identified 3 weeks later (20). After withdrawal the amniotic fluid volume returned to normal over 2 weeks. There were no adverse neonatal renal effects. 

Several studies have shown that the use of indometacin as a tocolytic agent is associated with severe adverse effects in the fetus (for example fetal ductal constriction, oligohydramnios), which limit this indication (SEDA-16, 108) (225). 

Magnesium sulfate may be used in an intravenous infusion as a tocolytic agent. Its mechanism of action is to suppress nerve impulses to the uterine smooth muscles by antagonizing intracellular calcium. Maternal side effects are rare but can include pulmonary edema. At toxic levels, hypotension, muscle paralysis, tetany, cardiac arrest, and respiratory depression may occur. ... 

Terbutaline, a bronchodilator (5 mg given p.o. at 6 hour intervals 3 times during waking hours), is indicated for rehef of bronchospasm in patients with reversible obstructive airway disease (see Figure 94) and terbutaline, a tocolytic agent (10 mcg/minutes fV), is also used in managing premature labor. 

Which assessment data would warrant immediate intervention for the client in labor who is receiving an oxytocin (Pitocin) drip, a tocolytic agent ... 

D. Use in pregnancy. FDA category A. Magnesium sulfate is commonly used as a tocolytic agent for premature labor (see p 405). 

In veterinary medicine clenbuterol is used for similar effects in horses with respiratory disease where it is given orally or by injection. It is also used as a tocolytic agent in cattle to delay delivery to prepare the birth canal, to act as an aid to obstetrical procedures, to relax the uterus for caesarean section, to delay and programme delivery, to facilitate the replacement of a prolapsed uterus and... 

In human medicine, isoxsuprine has been used for the treatment of Raynaud s phenomenon. However, its major use has been as a tocolytic agent and for the prevention of preterm labour. It has also been used in the treatment of cardiovascular disease. Unfortunately, the use of isoxsuprine... 

G. Falkay and L. Kovacs, Affinity of tocolytic agents on human placental and myometrial beta-adrenergic receptors, J. Perinat. Med., 1986, 14, 109-113. 

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