Medication Dosage by Weight Calculator

Important: Always verify dosing with a healthcare provider or pharmacist before administering any medication.
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Understanding Weight-Based Medication Dosing

Weight-based dosing (mg/kg dosing) is a method of calculating medication doses based on the patient's body weight. This approach is particularly important in pediatric medicine, oncology, and critical care, where precise dosing is essential for safety and efficacy.

How Weight-Based Dosing Works

The basic formula for weight-based dosing is:

Dose = Weight (kg) x Dose (mg/kg)

For example, if a medication is dosed at 10 mg/kg and the patient weighs 25 kg, the calculated dose would be 250 mg.

Why Weight-Based Dosing Is Important

Pediatric Patients

Children have different metabolic rates and body compositions than adults. Fixed adult doses can be dangerous or ineffective in children, making weight-based calculations essential.

Variable Body Sizes

Even among adults, body weight varies significantly. Weight-based dosing helps ensure that each patient receives an appropriate amount of medication relative to their size.

Narrow Therapeutic Window

Some medications have a small range between effective and toxic doses. Precise weight-based dosing helps maintain drug levels within the therapeutic range.

Common Medications Using Weight-Based Dosing

  • Antibiotics: Amoxicillin, Azithromycin, Cephalosporins
  • Pain Medications: Ibuprofen, Acetaminophen
  • Anticoagulants: Heparin, Enoxaparin
  • Chemotherapy: Most oncology drugs
  • Anesthetics: Propofol, Ketamine
  • Anticonvulsants: Phenytoin, Valproic Acid

Dosing Frequency Abbreviations

  • QD: Once daily (quaque die)
  • BID: Twice daily (bis in die)
  • TID: Three times daily (ter in die)
  • QID: Four times daily (quater in die)
  • Q4H: Every 4 hours
  • Q6H: Every 6 hours
  • PRN: As needed (pro re nata)

Important Considerations

  • Always check the specific medication's prescribing information
  • Some medications have maximum doses regardless of weight
  • Renal and hepatic function may require dose adjustments
  • Obese patients may require adjusted body weight calculations
  • Always double-check calculations before administration

Medical Disclaimer

This calculator is for educational and informational purposes only. It should NOT be used as the sole basis for medical decisions or medication administration. Always consult with a qualified healthcare provider, pharmacist, or use verified clinical resources before administering any medication. Dosing errors can cause serious harm or death. The creators of this calculator assume no liability for any adverse effects resulting from the use of information provided.

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