Epistemis

Antenatal Corticosteroids

  • Critical Obstetric Therapies

Betamethasone phosphate/acetate / Dexamethasone phosphate (e.g. *Celestone Cronodose*).

Mechanism

Mechanism of Action

Betamethasone and Dexamethasone are high-affinity fluorinated synthetic glucocorticoids that act as direct inducers of the synthesis and secretion of pulmonary surfactant factor (surfactant) in the fetus.

Physiology of Fetal Alveolar Maturation

1. Resistance to inactivation by 11β-HSD: Unlike endogenous corticosteroids, the fluorinated glucocorticoids betamethasone and dexamethasone are not significantly degraded by the placental enzyme 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2), so they cross the placental barrier freely and with high fetal bioavailability.
2. Activation of Glucocorticoid Receptors: In the fetal lungs, they bind to the cytoplasmic glucocorticoid receptor (GR) on the type II pneumocyte cells.
3. Surfactant Induction: The receptor-ligand complex stimulates the transcription of mRNA that codes for specific surfactant proteins (SP-A, SP-B and SP-C) and key enzymes of the phospholipid synthesis pathway (dipalmitoylphosphatidylcholine).
4. Structural changes: They accelerate the remodeling of collagen fibrils in the interstitial matrix, reducing the thickness of the alveolocapillary barrier and promoting the pulmonary transition from the canalicular phase to the final saccular phase, preparing the fetus for postpartum air ventilation.

Pharmacokinetics

Pharmacokinetics

  • Rout of administration: Exclusively deep intramuscular (injection into the gluteus or maternal deltoid).
  • Absorption: Fast. The usual betamethasone formulation associates a soluble, ultra-rapidly absorbed sodium phosphate salt (which reaches the fetal serum peak within 1 to 2 hours) combined with an insoluble acetate salt of slow and sustained absorption over 24 hours.
  • Metabolism: Maternal liver clearance through minor conjugation reactions.
  • Half-life (t1/2): Maternal approx. 5 to 6 hours; The biological half-life is prolonged in the fetus until 36 hours after crossing the placenta.
  • Excretion: Renal in the form of inactive metabolites.

Indicators and dose

Indications

  • Prevention of neonatal morbidity and mortality associated with Respiratory Distress Syndrome (RDS) due to surfactant deficiency (Hyaline Membrane Disease) in pregnant women with a diagnosis of imminent preterm birth between 24 and 34 complete weeks of gestation.
  • Reduced risk of necrotizing enterocolitis (NEC), cerebral intraventricular hemorrhage (IVH), and neonatal death in premature newborns.
  • Optional late prophylaxis: In women scheduled for elective cesarean section between weeks 37.0 and 38.6 of gestation, to reduce transient tachypnea of the newborn.

Dosage and Regimes of Choice

Only a single complete lung maturation cycle should be administered. Repeated multiple weekly rescue cycles are not recommended due to the risk of impaired neurodevelopment and low fetal birth weight:

Betamethasone Regimen (Of Choice)

Two IM doses spaced 24 hours apart:

  • 12 mg deep IM every 24 hours for 2 consecutive doses (total cumulative dose of 24 mg).
  • Profile with lower incidence of reported neonatal neurological adverse effects.
Dexamethasone Regimen (Alternative)

Four IM doses at short intervals:

  • 6 mg deep IM every 12 hours for a period of 4 consecutive doses (total cumulative dose of 24 mg).
  • It is reserved if betamethasone is not available.

Pregnancy and Breastfeeding

FDA Category C. Suitable formal indication for the prophylaxis of imminent preterm birth with an indisputable benefit on the survival of the preterm newborn. Compatible with puerperal breastfeeding.

Security

Contraindications

  • Confirmed active intrauterine infection (severe active chorioamnionitis, where immunosuppression by glucocorticoids can aggravate sepsis).
  • Untreated active maternal tuberculosis.
  • Known hypersensitivity to the active ingredients.

Adverse Effects (ADR)

  • Transient maternal hyperglycemia: Elevation of maternal blood glucose that lasts between 48 and 72 hours after the start of the cycle (corticosteroids stimulate maternal hepatic gluconeogenesis; requires strict monitoring and insulin adjustment in diabetic pregnant women).
  • Maternal transient leukocytosis: Marginal elevation of peripheral circulating leukocytes secondary to demarginalization of vascular mucus, without real infectious origin.
  • Transient fetal effects: Transient decrease in the variability of fetal heart rate and respiratory movements in the biophysical ultrasound profile between 24 and 48 hours post-infusion of the mother, without real well-being pathology.

Epistemis is educational review material. It is not a medical device, does not diagnose or prescribe treatment, and does not replace formal medical training, current clinical guidelines, or professional clinical judgment.

PreviousGestational Diabetes
System
Gynecology and Obstetrics
Cluster
Critical Obstetric Therapies
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