MEDICALMedication DosingHealth Calculator
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Medication Dosage Calculator

Calculate medication dosages based on weight, age, and indication. Accurate dosing is critical — medication errors affect 1.5 million Americans annually. This calculator supports mg/kg and mg/m² dosing methods.

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Calculate medication dosages using weight-based, BSA-based, or fixed dosing. Includes renal and hepatic adjustments.

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Why: Calculate medication dosages using weight-based, BSA-based, or fixed dosing.

How: Includes renal and hepatic adjustments.

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For weight-based
For BSA-based
For fixed dosing
For liquid
For tablets

Medical Disclaimer: This calculator is for educational purposes only. All medication doses must be verified by a qualified healthcare professional before administration.

Please enter a valid weight

For informational purposes only — not medical advice. Consult a healthcare professional before acting on results.

Medication dosing determines the appropriate amount of a drug to achieve therapeutic effect while minimizing toxicity. Weight-based (mg/kg) and BSA-based (mg/m²) methods are standard. Medication errors affect 1.5 million Americans annually. Accurate dosing is critical in pediatrics and for narrow therapeutic index drugs.

1.5M
Med errors/year (US)
mg/kg
Pediatric standard
25-50%
Renal reduction
BSA
Chemo dosing

Sources: WHO, CDC, FDA, Lexicomp

Key Takeaways

  • • Weight-based dosing: Dose = Weight (kg) × mg/kg
  • • BSA (Mosteller): √(H cm × W kg / 3600)
  • • Always apply renal/hepatic adjustments when indicated
  • • Verify against max single and max daily dose limits

Did You Know?

🔢 1.5 million Americans experience medication errors annually
📊 Pediatric doses often use mg/kg; adults may use fixed dosing
💡 BSA dosing used for chemotherapy and immunosuppressants
🌍 WHO provides weight-based dosing for many essential medicines
📈 Renal impairment (CrCl <60) requires dose reduction for many drugs
🎯 Use oral syringes for liquid doses—household spoons are inaccurate

How Does Dosing Work?

Weight-Based

Dose = Weight (kg) × Dose per kg. Standard for pediatrics, antibiotics, anticoagulants.

BSA-Based

BSA = √(H×W/3600). Dose = BSA × mg/m². Used for chemotherapy, methotrexate.

Fixed Dose

Standard amount regardless of weight. Common for wide therapeutic index drugs.

Expert Tips

Use recent weight for pediatric dosing—reweigh if uncertain
Apply 25-50% renal reduction when CrCl <60 mL/min
Use ideal or adjusted body weight for obese patients on weight-based drugs
Double-check liquid volumes with pharmacy or drug reference

Dosing Method Comparison

MethodWhen to UseExamples
Weight-basedPediatrics, antibioticsAmoxicillin, Vancomycin
BSA-basedChemotherapyDoxorubicin, Methotrexate
FixedAdult chronic medsMetformin, Lisinopril

Frequently Asked Questions

What is weight-based dosing?

Weight-based dosing calculates medication amounts per kilogram of body weight (mg/kg). It's the standard for pediatric and weight-sensitive drugs. Example: Amoxicillin 40 mg/kg/day for a 20 kg child = 800 mg/day.

How is BSA-based dosing calculated?

BSA (body surface area) uses the Mosteller formula: √(height cm × weight kg / 3600). Dose = BSA × mg/m². Used for chemotherapy and narrow therapeutic index drugs.

When should renal dose adjustment be applied?

Renal adjustment is needed when CrCl &lt;90 mL/min for many drugs. Moderate impairment (CrCl 30-59) typically requires 25-50% dose reduction. Consult drug-specific guidelines.

What is the maximum single dose for amoxicillin?

Adult max single dose is typically 500-1000 mg depending on indication. Pediatric max is often 500 mg per dose. Always verify against current prescribing information.

How do I convert liquid concentration to volume?

Volume (mL) = Dose (mg) ÷ Concentration (mg per 5 mL) × 5. For 250 mg/5 mL suspension, 500 mg dose = 10 mL. Use an oral syringe for accuracy.

Can this calculator replace medical advice?

No. This tool is for educational purposes only. All medication doses must be verified by a qualified healthcare professional before administration.

Key Statistics

1.5M
Med errors/year
mg/kg
Pediatric standard
25-50%
Renal reduction
BSA
Chemo dosing

Official Data Sources

WHO Model List ↗
Essential medicines dosing
Lexicomp ↗
Drug dosing reference
FDA Drug Labels ↗
Prescribing information
CDC Antibiotic Use ↗
Antimicrobial stewardship

⚠️ Disclaimer: This calculator is for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. All medication doses must be verified by a qualified healthcare professional before administration.

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