Complete drug dose calculation in pediatrics
Reading File
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Reading File
Finding Sources
Reading File
Finding Sources
Reading File
Finding Sources
Reading File
Finding Sources
Reading File
This is very rich content - the file was truncated because it's so large. I have everything I need to write a comprehensive, well-structured answer. Let me now compile the complete guide.
Complete Drug Dose Calculation in Pediatrics
Source: The Harriet Lane Handbook, 23rd ed. (Johns Hopkins Hospital) - the gold-standard pediatric clinical reference
1. Fundamental Principles of Pediatric Dosing
Pediatric drug dosing is weight-based, not age-based. Most drugs are dosed in mg/kg or mcg/kg, with a maximum ("cap") dose that prevents overdosing heavier children. Always:
- Weigh the child in kilograms (never in pounds without converting: kg = lb ÷ 2.2)
- Calculate the dose: Dose (mg) = Weight (kg) × Dose (mg/kg)
- Compare to the maximum dose and use whichever is lower
- Check the concentration of the available formulation, then calculate the volume to administer
2. Body Surface Area (BSA) Method
Some drugs (chemotherapy, certain antibiotics, some hormones) are dosed by BSA in m² rather than weight.
Mosteller Formula (most common):
BSA (m²) = √[ Height (cm) × Weight (kg) / 3600 ]
West Nomogram:
Alternatively use the BSA nomogram (Fig 30.1, Harriet Lane): draw a line from height to weight and read BSA at the intersection with the center column.
Dose = BSA (m²) × Dose per m²
3. Key Dose Calculation Steps (Step-by-Step)
Step 1: Confirm weight in kg
Step 2: Identify the drug's dose (mg/kg or mcg/kg or mg/m²)
Step 3: Calculate: Dose = Weight × mg/kg
Step 4: Check against maximum dose → use the lower value
Step 5: Identify available concentration (mg/mL)
Step 6: Volume (mL) = Dose (mg) ÷ Concentration (mg/mL)
Step 7: Double-check with a second provider (especially for high-alert drugs)
4. Age-Based Estimation Formulas (When Exact Weight is Unknown)
Estimated Weight:
| Age | Formula |
|---|---|
| Term newborn | ~3.5 kg |
| 3–12 months | Age (months) + 9 / 2 |
| 1–5 years | (2 × Age in years) + 8 |
| 6–12 years | (3 × Age in years) + 7 |
| Adolescent | Use actual weight |
Broselow Tape:
In emergencies, the color-coded Broselow-Luten tape (placed alongside the patient from head to heel) provides weight estimate and pre-calculated doses for resuscitation drugs. This is the recommended approach in pediatric codes.
5. Pediatric Resuscitation Medications (TABLE 1.1, Harriet Lane)
These are critical doses used in cardiac arrest and emergencies:
| Medication | Indication | Dose | Max Dose | Route |
|---|---|---|---|---|
| Adenosine | SVT (AV node reentry) | 0.1 mg/kg (1st), 0.2 mg/kg (2nd), 0.3 mg/kg (3rd) | 6 mg / 12 mg / 12 mg | IV rapid push |
| Amiodarone | Shock-refractory VF/pVT | 5 mg/kg over 20-60 min (with pulse) or push (no pulse) | 300 mg | IV/IO |
| Atropine | Vagal bradycardia, AV block, cholinergic toxicity | 0.02 mg/kg | 0.5 mg/dose; min 0.1 mg | IV/IO/IM/ET |
| Calcium chloride | Hypocalcemia, hyperkalemia, Ca-channel blocker OD | 20 mg/kg over 5 min | 1 g | IV/IO |
| Dextrose | Documented hypoglycemia | 0.5-1 g/kg: Neonates: 5-10 mL/kg D10W; Infants/children: 2-4 mL/kg D25W; Adolescents: 1-2 mL/kg D50W | - | IV/IO |
| Epinephrine | Asystole, PEA, VF, bradycardia | 0.01 mg/kg IV/IO (0.1 mg/mL concentration); 0.1 mg/kg ET (1 mg/mL) | 1 mg IV; 2.5 mg ET | IV/IO/ET |
| Lidocaine | VF/pVT, wide complex tachycardia | 1 mg/kg IV/IO bolus | 100 mg | IV/IO |
| Magnesium sulfate | Torsades de pointes, hypomagnesemia, status asthmaticus | 25-50 mg/kg over 15-30 min | 2 g | IV/IO |
| Naloxone | Opioid reversal | 0.01-0.1 mg/kg | 2 mg/dose | IV/IO/IM/IN |
| Sodium bicarbonate | Metabolic acidosis, hyperkalemia, TCA OD | 1 mEq/kg | - | IV/IO slow push |
Epinephrine infusion: 0.05-2 mcg/kg/min
6. Rapid Sequence Intubation (RSI) Medications (TABLE 1.2, Harriet Lane)
Adjuncts:
| Drug | Dose | Indication |
|---|---|---|
| Atropine | 0.02 mg/kg IV (max 0.5 mg) | Pre-RSI in infants, prevent bradycardia |
| Glycopyrrolate | 0.004-0.01 mg/kg IV (max 0.1 mg) | Decrease secretions, less tachycardia than atropine |
| Lidocaine | 1 mg/kg IV (max 100 mg) | Elevated ICP, status asthmaticus |
Induction Agents:
| Drug | Dose | Notes |
|---|---|---|
| Etomidate | 0.3 mg/kg IV (max 20 mg) | Minimal CV effect; avoid in septic shock |
| Ketamine | 1-2 mg/kg IV (max 150 mg); 4-6 mg/kg IM | Drug of choice in asthma, shock |
| Fentanyl | 1-5 mcg/kg slow IV (max 100 mcg) | Use in shock |
| Midazolam | 0.05-0.1 mg/kg IV/IM (max 6-10 mg by age) | Mild shock |
| Propofol | 1-3 mg/kg IV | Do NOT use in hemodynamic instability |
Paralytics:
| Drug | Dose | Notes |
|---|---|---|
| Succinylcholine | 1-2 mg/kg IV (infants: 2 mg/kg); 4 mg/kg IM | Depolarizing; check for contraindications (hyperkalemia, myopathies) |
| Rocuronium | 0.6-1.2 mg/kg IV | Non-depolarizing; reversible with sugammadex |
| Vecuronium | 0.1 mg/kg IV | Non-depolarizing |
7. Anaphylaxis - Emergency Epinephrine Dosing
| Patient | IM Dose | Auto-injector |
|---|---|---|
| Children (any weight) | 0.01 mg/kg of 1 mg/mL solution | - |
| 7.5 to <15 kg | - | 0.1 mg |
| 15 to <30 kg | - | 0.15 mg |
| ≥30 kg | Max 0.3 mg | 0.3 mg |
Inject into the midanterolateral thigh. Repeat every 5-15 minutes as needed.
8. Fluid Dosing
Resuscitation Bolus:
- 20 mL/kg of isotonic crystalloid (normal saline or lactated Ringer's) IV/IO - reassess and repeat as needed
- In hemorrhagic shock: use blood products preferentially
Maintenance Fluids - Holliday-Segar Formula:
| Weight | Rate |
|---|---|
| First 10 kg | 100 mL/kg/day (= 4 mL/kg/hr) |
| Next 10 kg (10-20 kg) | + 50 mL/kg/day (= + 2 mL/kg/hr) |
| Each kg above 20 kg | + 20 mL/kg/day (= + 1 mL/kg/hr) |
Example - 25 kg child:
- 1000 mL (first 10 kg) + 500 mL (next 10 kg) + 100 mL (5 kg × 20) = 1600 mL/day = 67 mL/hr
Shortcut (4-2-1 rule for mL/hr):
- 4 mL/kg/hr for first 10 kg
- +2 mL/kg/hr for 10-20 kg
- +1 mL/kg/hr above 20 kg
9. Neonatal-Specific Considerations
- Premature and term neonates have immature renal and hepatic function - dosing intervals are often extended
- Dextrose for hypoglycemia: 5-10 mL/kg of D10W (not D50W - risk of vascular injury)
- GFR is very low at birth and matures over weeks to months - adjust doses of renally cleared drugs (e.g., aminoglycosides, vancomycin)
- Volume of distribution is higher due to higher body water content - some drugs need higher mg/kg doses
10. Safe Prescribing Rules (Joint Commission "Do Not Use" List)
| Do NOT write | Problem | Write instead |
|---|---|---|
| U (unit) | Mistaken for "0" or "4" | Write "unit" |
| IU | Mistaken for IV or 10 | Write "International Unit" |
| QD, q.d. | Mistaken for each other | Write "daily" |
| Trailing zero (1.0 mg) | Decimal missed → 10× OD | Write "1 mg" |
| Naked decimal (.5 mg) | Decimal missed → 5× OD | Write "0.5 mg" |
| MS, MSO4, MgSO4 | Morphine vs. magnesium confusion | Write out full name |
11. High-Alert Medications in Pediatrics
Extra verification is required for:
- Opioids (morphine, fentanyl) - weight-based, easy to overdose
- Insulin - always confirm units vs. mL
- Heparin - units/kg/hr infusion
- Chemotherapy - BSA-based, institutional protocols mandatory
- Concentrated electrolytes (KCl, NaCl 3%) - never give undiluted
- Digoxin - narrow therapeutic index; different loading/maintenance doses by age
12. Quick Reference - Common Pediatric Doses
| Drug | Dose | Max | Route |
|---|---|---|---|
| Acetaminophen | 10-15 mg/kg every 4-6 hr | 75 mg/kg/day or 4 g/day | PO/PR/IV |
| Ibuprofen | 5-10 mg/kg every 6-8 hr | 40 mg/kg/day or 2.4 g/day | PO (≥6 months) |
| Amoxicillin | 25-45 mg/kg/day ÷ every 8-12 hr | 3-4 g/day | PO |
| Ceftriaxone | 50-100 mg/kg/day ÷ every 12-24 hr | 4 g/day | IV/IM |
| Morphine | 0.05-0.1 mg/kg every 2-4 hr PRN | 15 mg/dose | IV slow push |
| Albuterol nebulized | 0.15 mg/kg (min 2.5 mg) | 5 mg | Inhaled |
| Ondansetron | 0.1-0.15 mg/kg | 4 mg (2-12 yr); 8 mg (>12 yr) | IV/PO |
| Dexamethasone (croup) | 0.6 mg/kg single dose | 10-16 mg | PO/IM/IV |
| Diazepam (seizure) | 0.2-0.5 mg/kg | 10 mg/dose (IV) | IV/PR |
| Lorazepam (seizure) | 0.05-0.1 mg/kg | 4 mg/dose | IV/IO |
13. Practical Worked Examples
Example 1: Febrile 3-year-old, weighs 14 kg
- Ibuprofen 10 mg/kg PO
- Dose = 14 × 10 = 140 mg
- Children's ibuprofen 100 mg/5 mL → Volume = 140 ÷ 20 = 7 mL
Example 2: Septic infant (6 months, 7 kg) - ceftriaxone 100 mg/kg IV
- Dose = 7 × 100 = 700 mg
- Max = 4 g → 700 mg is below max ✓
- Available: 500 mg/5 mL → Volume = 700/100 = 7 mL
Example 3: Cardiac arrest in 20 kg child - epinephrine IV
- Dose = 0.01 mg/kg = 0.01 × 20 = 0.2 mg
- Available: 0.1 mg/mL (1:10,000) → Volume = 0.2/0.1 = 2 mL
Example 4: Status epilepticus, 30 kg child - lorazepam IV
- Dose = 0.1 mg/kg = 0.1 × 30 = 3 mg
- Max = 4 mg → 3 mg is below max ✓
- Available: 2 mg/mL → Volume = 3/2 = 1.5 mL
Key Takeaways
- Always use mg/kg and never skip checking the maximum dose
- Use actual weight when available; use Broselow tape in emergencies
- BSA-based dosing is reserved for chemotherapy and select drugs
- The 4-2-1 rule is the standard for maintenance fluid calculation
- Avoid dangerous abbreviations - decimal errors are a leading cause of pediatric medication errors
- Two-provider verification is standard for high-alert medications
- Neonates require dose and interval adjustments due to immature organ function
- The Harriet Lane Handbook, 23rd ed. (Johns Hopkins), Chapter 1 & Chapter 30 (Formulary)
This is a shared conversation. Sign in to Orris to start your own chat.