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Tocolytic

Tocolytics are medications used to suppress premature labor (from the Greek tokos, childbirth, and lytic, capable of dissolving). They are given when delivery would result in premature birth. The therapy also buys time for the administration of betamethasone, a glucocorticoid drug which greatly accelerate fetal lung maturity, but takes one to two days to work.

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The suppression of contractions is often only partial and tocolytics can only be relied on to delay birth for several days. Depending on the tocolytic used the mother or fetus may require monitoring, as for instance blood pressure monitoring when nifedipine is used as it reduces blood pressure. In any case the risk of preterm labor alone justifies hospitalization.

Types of agents

Various types of agents are used, with varying success rates and side effects. Some medications are not specifically FDA approved for use in stopping uterine contractions in preterm labor, instead being used off label. Nifedipine is one of the most commonly used tocolytic agents[1].

Examples:

Magnesium sulfate
ritodrine (Yutopar)
fenoterol
nifedipine (Procardia, Adalat)
atosiban
salbutamol
indomethacin
terbutaline (Brethine)

Ethyl alcohol was frequently prescribed as a tocolytic in the mid-20th century, but later double-blind studies^[2] found it was not effective.

Contraindications to Tocolysis

Several factors may contraindicate delaying birth with the use of tocolytic medications. ^[3]

Fetus is older than 37 weeks gestation
Fetus weighs more than 2500g or has IUGR
Fetus is in acute distress or has died (or has a fatal anomaly)
Dilation is greater than 4 cm
Chorioamnionitis or intrauterine infection is present
Mother has severe Pregnancy-induced hypertension, eclampsia, active vaginal bleeding, a cardiac disease, or another condition which indicates that the pregnancy should not continue.