Medical Dosage & Volume Calculator
Calculate precise pediatric and adult medication dosages based on patient weight and stock concentration.
Total Required Dose: 0 mg
Volume to Administer: 0 ml
Concentration: 0 mg/ml
How to Calculate Drug Dosages
In clinical settings, medication safety is paramount. The primary method for calculating dosages, especially in pediatrics, involves weight-based calculations. This ensures the patient receives a therapeutic amount of medication without toxicity.
The Core Formula
The standard formula used by healthcare professionals is often referred to as "Desired over Have":
(Desired Dose / Dose on Hand) × Volume = Amount to Administer
When dealing with weight-based prescriptions (mg/kg), the process follows two steps:
- Calculate Total Dose (mg): Multiply the patient's weight in kilograms by the prescribed dose per kilogram.
- Calculate Liquid Volume (ml): Divide the total required dose by the concentration of the medication on hand.
Practical Example
Let's look at a realistic scenario for Paracetamol (Acetaminophen) administration:
- Patient: Child weighing 20 kg.
- Prescription: 15 mg/kg.
- Stock Strength: 120 mg in 5 ml.
Step 1: 20 kg × 15 mg/kg = 300 mg (Total Dose).
Step 2: 300 mg / (120 mg / 5 ml) = 300 / 24 = 12.5 ml.
Important Clinical Considerations
| Measurement | Requirement |
|---|---|
| Weight | Always use kilograms (kg). If weight is in lbs, divide by 2.2. |
| Rounding | Generally, volumes under 1 ml are rounded to two decimal places; over 1 ml to one decimal place. |
| Double Check | Always verify high-alert medications (e.g., insulin, heparin) with a second clinician. |
Standard Units in Drug Calculations
Understanding unit conversion is essential to prevent medication errors:
- 1 gram (g) = 1,000 milligrams (mg)
- 1 milligram (mg) = 1,000 micrograms (mcg)
- 1 liter (L) = 1,000 milliliters (ml)