What is the appropriate prednisone dosage for a 40‑lb (≈18‑kg) child?

Prednisone Dosing for a 40 lb (≈18 kg) Child

For a 40 lb (18 kg) child, give prednisone 1–2 mg/kg/day (18–36 mg daily) as a single morning dose, with the exact dose and duration determined by the underlying condition being treated; for most acute conditions requiring high-dose therapy, use 36 mg daily (2 mg/kg/day) with a maximum ceiling of 60 mg/day. 1, 2, 3

Weight-Based Dosing Framework

• Standard pediatric dosing range: 1–2 mg/kg/day translates to 18–36 mg daily for an 18 kg child, administered as a single morning dose before 9 AM to minimize hypothalamic-pituitary-adrenal (HPA) axis suppression and mimic physiologic cortisol secretion. 1, 2, 3

• Body surface area (BSA) alternative: If using BSA-based dosing (60 mg/m²/day), a simplified weight-based equation [2 × weight in kg + 8] yields approximately 44 mg daily for this child, which provides more accurate dosing than simple mg/kg calculations, especially in younger children. 4, 5

• Maximum daily dose: The absolute ceiling is 60 mg/day regardless of weight-based calculations, though this 18 kg child will not approach that limit. 1, 2

Condition-Specific Dosing

Acute Asthma Exacerbations

• Dose: 18–36 mg once daily (1–2 mg/kg/day) for 3–10 days; most commonly prescribe 30–36 mg daily for 5–7 days. 1, 2, 6
• No taper required: Courses ≤7–10 days can be stopped abruptly without risk of adrenal insufficiency. 2, 6

Nephrotic Syndrome (First Episode)

• Induction phase (4–6 weeks): 36 mg once daily (2 mg/kg/day, max 60 mg) as a single morning dose; using the BSA equation yields 44 mg daily [2 × 18 + 8], which may reduce the risk of frequent relapses compared to strict weight-based dosing. 1, 2, 3, 4, 5
• Alternate-day phase (2–5 months): Switch to 27–30 mg on alternate days (1.5 mg/kg or 40 mg/m², max 40 mg) with gradual taper; the BSA equation [weight + 11] yields 29 mg for alternate-day dosing. 2, 3, 4
• Minimum total duration: At least 12 weeks of corticosteroid therapy to achieve sustained remission. 2

Autoimmune Hepatitis

• Initial induction: 36 mg once daily (2 mg/kg/day, max 60 mg) for 2 weeks, then taper over 6–8 weeks to a maintenance dose of 1.8–3.6 mg daily (0.1–0.2 mg/kg/day). 1, 2
• Adjunctive therapy: Add azathioprine 1–2 mg/kg/day to allow earlier steroid tapering and reduce cumulative steroid exposure. 1

Moderate to Severe Inflammatory Conditions

• Moderate disease: 5.4 mg daily (0.3 mg/kg/day). 1
• Moderate-severe disease: 9 mg daily (0.5 mg/kg/day). 1
• Severe disease: 13.5–18 mg daily (0.75–1 mg/kg/day). 1, 2

Tapering Protocol

• Short courses (≤7–10 days): Stop abruptly without taper. 2, 6

• Courses >10–14 days: Implement structured tapering to prevent adrenal insufficiency:

  1. Reduce by 5 mg weekly until reaching 10 mg/day
  2. Reduce by 2.5 mg weekly until reaching 5 mg/day
  3. Reduce by 1 mg monthly until discontinuation 1, 2

• Alternate approach: Reduce by 25–33% at appropriate intervals once clinical response is achieved. 1, 3

Critical Dosing Considerations

• Overweight children: Calculate dose based on ideal body weight, not actual weight, to avoid excessive steroid exposure and increased side effects. 1, 2, 3

• Underdosing risk: Weight-based dosing (mg/kg) systematically underdoses younger children compared to BSA-based dosing; this underdosing increases the risk of frequent relapses in nephrotic syndrome by approximately 8–17%. 4, 5

• Administration timing: Give as a single morning dose before 9 AM to align with natural cortisol rhythm and minimize HPA axis suppression; avoid afternoon dosing unless behavioral side effects (hyperactivity, emotional lability) necessitate it. 1, 2, 3

Monitoring and Prevention

• Bone health: Initiate calcium and vitamin D supplementation immediately when starting therapy, especially for courses anticipated to last >2–3 weeks. 1, 2

• Growth and metabolic effects: Monitor growth parameters, blood pressure, weight gain, Cushingoid features, and signs of hyperglycemia regularly throughout treatment. 1, 3

• HPA axis suppression: Doses >5 mg/day prednisone-equivalent for >10–14 days carry risk of adrenal suppression; provide stress-dose steroids during intercurrent illness if prolonged therapy has been used. 2

Common Pitfalls to Avoid

• Do not use simple mg/kg dosing for nephrotic syndrome: The BSA-based equation [2 × weight + 8] provides more accurate dosing and reduces relapse risk. 4, 5

• Do not taper short courses: Courses <7–10 days can be stopped abruptly; unnecessary tapering prolongs steroid exposure without benefit. 2, 6

• Do not exceed 60 mg/day ceiling: Even if calculations suggest higher doses, the maximum is 60 mg/day for standard therapy. 1, 2

• Do not dose obese children by actual weight: Use ideal body weight to prevent overdosing and minimize adverse effects. 1, 2, 3