Dexamethasone

Class and Basic Properties

• The Washington Manual of Medical Therapeutics, p. 975

Formulations and Trade Names

Pharmacokinetics

• Metabolism: Substrate of CYP3A4 and P-glycoprotein; moderate inducer of CYP3A4
• Half-life: Long biological half-life (~36-54 hours), allowing once-daily or less frequent dosing in many settings
• Distribution: Widely distributed, crosses the blood-brain barrier and placenta

Clinical Indications and Dosing

Anti-inflammatory / Immunosuppression

• Adults: 0.75-9 mg/24 hr PO/IV/IM divided Q6-12 hr
• Children: 0.08-0.3 mg/kg/24 hr PO/IV/IM divided Q6-12 hr

Croup (laryngotracheobronchitis)

• Infants/children: 0.6 mg/kg/dose PO/IV/IM x 1 dose (max 16 mg) -- single dose is highly effective

Asthma Exacerbation

• Children: 0.6 mg/kg/dose (max 16 mg) PO/IV/IM Q24h x 1-2 doses

Airway Edema / Pre-extubation

• 0.5 mg/kg/dose (max 10 mg) IV/IM/PO Q6h x 6 doses, starting 6-12 hours before extubation

Cerebral Edema

• Loading: 1-2 mg/kg/dose IV/IM x 1
• Maintenance: 1-2 mg/kg/24 hr (limited data in pediatrics)

Antiemetic (chemotherapy-induced nausea)

• Initial: 10 mg/m²/dose IV (max 20 mg)
• Subsequent: 5 mg/m²/dose Q6h IV

Meningitis

• Dexamethasone given before antibiotics reduces neurologic sequelae of bacterial meningitis, especially pneumococcal. This is a well-established indication.
• Goldman-Cecil Medicine

Altitude Mountain Sickness (AMS) Prevention/Treatment

• 2 mg Q6h or 4 mg Q12h for prophylaxis; however, AMS can rebound rapidly upon discontinuation
• Rosen's Emergency Medicine, p. 518

Perioperative / Regional Anesthesia Adjuvant

• 4-10 mg IV in adults prolongs peripheral nerve blockade by ~4 hours with long-acting agents (e.g., bupivacaine) and reduces postoperative nausea. Can be given IV or perineurally (though perineural use is off-label).
• Miller's Anesthesia, 10e

Adrenal Insufficiency - Dexamethasone Suppression Test

• Standard 1 mg overnight suppression test: dexamethasone 1 mg at 11 PM, cortisol measured at 8 AM. Normal: cortisol <1.8 mcg/dL. Used to screen for hypercortisolism (Cushing syndrome).

Other Uses

• Nausea/vomiting (general antiemetic adjunct)
• Ophthalmic inflammation (uveitis, post-surgical, allergic conjunctivitis)
• Otitis externa (ophthalmic solution/suspension can be used)
• Fetal lung maturation in preterm labor (typically betamethasone preferred, but dexamethasone is an alternative)

Adverse Effects

• Calcium 1-1.5 g/day + Vitamin D 1000 IU/day from the start
• Bisphosphonate for bone protection
• Consider Pneumocystis jirovecii prophylaxis if on prednisone ≥20 mg (equivalent) for >1 month

Key Contraindications

• Active untreated systemic infections
• Fungal, viral, or mycobacterial ocular infections (for ophthalmic use)
• Not recommended for prevention/treatment of chronic lung disease in very-low-birth-weight infants (increased adverse events)

Important Drug Interactions

• CYP3A4 inducer: Can reduce plasma levels of CYP3A4 substrates (e.g., some antiretrovirals, immunosuppressants, hormonal contraceptives)
• P-glycoprotein substrate: affected by P-gp inhibitors/inducers
• NSAIDs: additive GI ulceration risk
• Vaccines: Immunosuppressive doses reduce response to live vaccines

Special Populations

• Pregnancy: Pharmacologic doses associated with decreased fetal growth, metabolic impairment, neuropsychiatric changes. Use with caution; betamethasone generally preferred for fetal lung maturation.
• Hyperglycemia: Consider alternative (lower glucocorticoid-potency) steroid when glucose control is a concern, since dexamethasone has potent glucose-elevating effects with no mineralocorticoid offset.
• Pediatrics: Not recommended for systemic use in prevention/treatment of chronic lung disease in very low birth weight infants.