Body Surface Area in Pediatric Drug Dosing
Weight alone is a blunt tool for pediatric dosing, especially in oncology. BSA better reflects metabolic rate and is mandatory for chemo. You'll see three formulas floating around; Haycock is what most institutions use.
BSA Calculation Formulas
Haycock equation works best under 40 kg:
BSA (m²) = 0.024265 × Weight (kg)^0.5378 × Height (cm)^0.3964
This came from cadaver data and is the pediatric oncology standard.
Mosteller is simpler and widely used because EHRs have it built in:
BSA (m²) = √[Height (cm) × Weight (kg) / 3600]
Good enough for quick calculations if you've got a kid over 20 kg. You'll notice it gives slightly different values than Haycock for younger kids.
DuBois is the old workhorse, still in some hospital protocols:
BSA (m²) = 0.007184 × Height (cm)^0.725 × Weight (kg)^0.425
Historically underestimates small children, which is why it's fallen out of favor.
Use BSA Calculator to run the numbers.
When You Actually Need BSA
Chemotherapy: Non-negotiable. The margin between efficacy and organ toxicity is razor-thin. A 10% overdose can mean life-threatening cardiotoxicity or hepatic failure. A 10% underdose means inadequate disease control. You're looking at stuff like doxorubicin 60–75 mg/m², cisplatin 75–100 mg/m², methotrexate 1–12 g/m².
High-dose CV drugs: Inotropes (dobutamine, milrinone) and vasodilators work better when normalized to BSA, more predictable hemodynamic response across different body sizes.
Dialysis: Small solute clearance targets need BSA adjustment.
Contrast media: Higher concentrations = higher nephrotoxicity risk; BSA dosing hedges that.
Use Chemo BSA Dosing to verify your chemo orders.
Parkland Formula: Burn Resuscitation
Burns are brutal. Too little fluid and you get shock; too much and you get pulmonary edema or abdominal compartment syndrome.
Fluid (mL) = 4 mL × TBSA (%) × Weight (kg), half given in first 8 hours, remainder over next 16
The key is getting TBSA right. Kids aren't little adults: the head represents a proportionally larger TBSA in infants (~18% in infants vs 9% in adults), while the legs are proportionally smaller (~14% each in infants vs 18% in adults). Use the Lund-Browder chart for accurate age-adjusted TBSA estimation.
Use Parkland Burns to estimate TBSA and plan fluids.
Obese Pediatric Dosing
For obese pediatric patients, using actual body weight can result in overdosing. Several approaches exist for estimating ideal or adjusted body weight. The Devine formula (originally derived for adults) uses height:
Males: IBW (kg) = 50 + 2.3 × [height (inches) – 60] Females: IBW (kg) = 45.5 + 2.3 × [height (inches) – 60]
Note this formula is only applicable to patients ≥5 feet (152 cm) tall. For younger or shorter children, BMI-based methods or institutional protocols for ideal body weight estimation should be used. Before dosing, always verify whether your protocol specifies actual weight, adjusted body weight, IBW, or BSA.
Use Ideal Body Weight for obese patients.
In Practice
- Verify the dosing standard in your protocol before you write the order
- For chemo: Always double-check your BSA calculation and have someone else verify it
- Document which formula you used
- Recalculate if the kid's gained or lost significant weight
- Use your EHR calculator if it's available and you trust it