Tocolysis

Adrenergic receptor agonists are also used to treat premature labour by causing uterine relaxation. Fenoterol and ritodrine are frequently used. The effectiveness of long-term tocolysis is controversial, since both desensitization of the receptors and the symptomatic nature of this treatment may limit their effects to 1-2 days according to one large study. 

Drugs most commonly used for acute tocolysis include magnesium sulfate, -adrenergic agonists, NSAIDs, and calcium channel blockers. 

Tocolysis. The uterine relaxant effect of P2-adrenoceptor agonists, such as terbutaline or fenoterol, can be used to prevent premature labor. Vasodilation Ltillmann, Color Atlas of Pharmacology (... 

Magnesium sulfate, applied intravenously is often used as tocolytic. The mechanism of action is not completely clear but might involve a competition with calcium on the cellular level. Precautions in the sense of magnesium plasma level monitoring must be taken in patients with renal insufficiency since this divalent kation is eliminated by the kidneys. Relatively high plasma concentrations are necessary to achieve a sufficient tocolysis. The relatively frequent side effects are respiratory depression, depressed reflexes, headaches, palpitation and skin flushing in the mother and muscle relaxation and, rarely, CNS depression in the fetus. 

Intravenous use of ethanol, while once widely employed to inhibit premature labor, is now of historical interest only. Ethanol inhibits oxytocin release from the pituitary and thus indirectly decreases myometrial contractility. Today, pz-adrenomimetics and magnesium sulfate have replaced ethanol for parenteral tocolysis. 

There is much debate as to the efficacy of magnesium sulfate. For effective inhibition of uterine activity, enough must be given to maintain a blood plasma level of at least 5.5 mEq/L. Even at this level, tocolysis may be hard to achieve. 

Which of the following is a special concern for the use of indomethacin for inducing labor (tocolysis) ... 

Rodts-PaleniJk S and Morrison JC. Tocolysis An update for the practitioner. Obstet Gynecol Surv 2002 1 127-131. 

Atosiban is an antagonist of the oxytocin receptor that has been approved outside the USA as a treatment for preterm labor (tocolysis). Atosiban is a modified form of oxytocin that is administered by IV infusion for 2-48 hours. In a small number of published clinical trials, atosiban appears to be as effective as B-adrenoceptor-agonist tocolytics and to produce fewer adverse effects. In 1998, the FDA decided not to approve atosiban based on concerns about efficacy and safety. 

Atosiban Blocks oxytocin receptors Decreased uterine contractions Tocolysis for preterm labor IV infusion Toxicity Concern about rates of infant death... 

Chandraharan E, Arulkumaran S Acute tocolysis. Curr Opin Obstet Gynecol 2005 17 151. [PMID 15758607]... 

For therapeutic purposes and under the control of a responsible veterinarian, the administration to farm animals of 17/3-estradiol, testosterone, and progesterone and derivatives that readily yield the parent compound on hydrolysis after absorption at the site of application may be authorized by the individual EU member states. Also, for therapeutic purposes, the administration of authorized veterinary medicinal products containing (i) allyl trenbolone, administered orally, or beta-agonists to equidae and pets, provided they are used in accordance with the manufacturer s instructions, (ii) beta-agonists, in the form of an injection to induce tocolysis in cows when calving may be authorized. Again, these veterinary medicinal products must be administered by a veterinarian under his direct responsibility. 

Indomethacin Tocolysis in preterm labor Rectal suppository Vaginal administration proved to be more effective than conventional rectal plus oral administration 335... 

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). 

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). 

ParUla BV, Grobman WA, Holtzman RB, Thomas HA, Dooley SL. Indomethacin tocolysis and risk of necrotizing enterocolitis. Obstet Gynecol 2000 96(l) 120-3. 

Gokay Z, Ozcan T, Copel JA. Changes in fetal hemodynamics with ritodrine tocolysis. Ultrasound Obstet Gynecol 2001 18(l) 44-6. 

Cao Z, Bideau R, Valdes R Jr, Eliii RJ. Acute hypermagnesemia and respiratory arrest following infusion of MgS04 for tocolysis. Clin Chim Acta 1999 285(l-2) 191-3. 

Lees CC, Lojacono A, Thompson C, Danti L, Black RS, Tanzi P, White IR, Campbell S. Glyceryl trinitrate and ritodrine in tocolysis an international multicenter randomized study. GTN Preterm Labour Investigation Group. Obstet Gynecol 1999 94(3) 403-8. 

Keirse MJNC. Indomethacin tocolysis in preterm labour. In Cochrane Library. CDROM and online versions. 

ShoU JS, Hughey MJ, Hrrschmann RA. Myotonic muscular dystrophy associated with ritodrine tocolysis. Am J Obstet Gynecol 1985 151(l) 83-6. 

Tocolytic therapy should not be used in cases of intrauterine infection, fetal distress, severe preeclampsia, vaginal bleeding, and maternal hemodynamic instability. The criteria for starting tocolysis are regular uterine contractions with cervical change. In women with cervical dilatation >3 cm, tocolytic therapy is less effective. ... 

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