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Pharmacology · Corticosteroids (glucocorticoids)

Betamethasone !

A potent, long-acting corticosteroid. Given to the mother before a preterm birth, it helps the baby's lungs mature.

Updated 2026-11-01

The figure shows dexamethasone in the ligand-binding pocket of the human glucocorticoid receptor; betamethasone, which differs from dexamethasone only in the orientation of one methyl group, binds the same pocket.

Target in 3D: Glucocorticoid receptor (GR), a nuclear receptor. PDB structure 1M2Z (RCSB PDB, public domain). View the structure at RCSB PDB

Mechanism of action

Betamethasone is a fluorinated glucocorticoid that binds the glucocorticoid receptor; the complex enters the nucleus, switches on anti-inflammatory genes and represses NF-κB and AP-1. It has practically no salt-retaining effect and a long duration. It crosses the placenta well, and in the fetal lung it speeds surfactant production and maturation.

  1. Betamethasone binds the glucocorticoid receptor
  2. The complex changes gene transcription in the nucleus
  3. Inflammatory mediators fall; in the fetal lung, surfactant rises

Pharmacokinetics

Absorption
IM injectable suspension (phosphate plus acetate), oral and topical forms
Distribution
Crosses the placenta more readily than cortisol, which suits fetal lung maturation
Half-life
Long-acting; the acetate part of the suspension is released slowly

Indications

  • Fetal lung maturation when preterm birth is expected
  • Rheumatic diseases and acute gouty arthritis (intra-articular or IM) Gout →
  • Severe allergic states, including allergic rhinitis Allergic rhinitis →
  • Inflammatory skin diseases (topical forms)

Adverse effects

Common

  • Hyperglycaemia, including in the mother after antenatal doses
  • Insomnia and mood changes
  • Pain or skin changes at the injection site
  • Skin thinning with topical use

Contraindications

  • Systemic fungal infections
  • Hypersensitivity to the product
  • Live or live attenuated vaccines during immunosuppressive doses

Key interactions

CYP3A4 inducers (rifampicin, phenytoin, carbamazepine, barbiturates)
Faster clearance and a weaker corticosteroid effect
Strong CYP3A4 inhibitors (ketoconazole)
Higher corticosteroid levels and more side effects
Aspirin and other NSAIDs
Higher risk of gastrointestinal ulcer and bleeding
Potassium-depleting drugs (loop or thiazide diuretics, amphotericin B)
Hypokalaemia; with digoxin, more risk of arrhythmia

What is monitored

  • Maternal glucose after antenatal doses, especially with diabetes
  • Blood pressure and weight
  • Potassium
  • Signs of infection

Administration and safety

  • The phosphate-acetate suspension is for IM or local injection only: never IV
  • The suspension is shaken before drawing it up
  • Epidural injection of corticosteroids has caused serious neurological events

Nursing care

  • For antenatal courses, record the time of each injection; the course is timed in relation to delivery
  • Check maternal glucose after the doses
  • Watch for infection: fever and other signs may be blunted
  • Watch mood and sleep; report agitation, depression or confusion

Pregnancy and breastfeeding

Used in pregnancy on purpose for fetal lung maturation when preterm birth is expected; other uses weigh benefit against risk.

Test yourself

Think of the answer, then tap the question to see it.

Why is betamethasone given to a mother at risk of preterm birth?

It crosses the placenta and speeds fetal lung maturation and surfactant production, lowering neonatal respiratory distress syndrome.

Why is the betamethasone phosphate-acetate suspension never given IV?

It is a particulate suspension for IM or local injection; the slowly released acetate particles are not meant for the bloodstream.

Which two common corticosteroids are stereoisomers?

Betamethasone and dexamethasone: they differ only in the orientation of the methyl group at carbon 16.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: Betamethasone Injection: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); DailyMed - BETAMETHASONE SODIUM PHOSPHATE AND BETAMETHASONE ACETATE injection, suspension (DailyMed (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); Farmacología básica y clínica (Katzung), 16.ª ed., cap. 39 (McGraw Hill, 2025).

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Representative model, for educational purposes only.