Accurate drug dosing is critical in healthcare to ensure therapeutic efficacy while minimizing adverse effects. This calculator helps determine the volume of a drug solution to administer based on patient weight, prescribed dosage, and drug concentration.
The Formula Explained
The calculation involves two main steps:
Calculate the Total Drug Amount Needed: This is determined by the patient's weight and the prescribed dosage per kilogram.
Total Drug Amount (mg) = Patient Weight (kg) * Drug Dosage (mg/kg)
Calculate the Volume to Administer: Once the total drug amount is known, we can use the drug's concentration to find the volume of the solution required.
Volume to Administer (mL) = Total Drug Amount (mg) / Drug Concentration (mg/mL)
Unit Conversions (Internal Handling)
This calculator handles common concentration units. Internally, it converts micrograms (mcg) and grams (g) to milligrams (mg) for consistent calculation:
1 mg = 1000 mcg
1 g = 1000 mg
The final volume is always presented in milliliters (mL).
Example Calculation
Let's consider a scenario:
A patient weighs 65 kg.
The prescribed drug dosage is 10 mg/kg.
The available drug concentration is 20 mg/mL.
Step 1: Calculate Total Drug Amount Total Drug Amount = 65 kg * 10 mg/kg = 650 mg
Step 2: Calculate Volume to Administer Volume to Administer = 650 mg / 20 mg/mL = 32.5 mL
Therefore, 32.5 mL of the drug solution should be administered.
Important Disclaimer
This calculator is a tool for informational purposes only and should not replace professional medical judgment. Always consult with a qualified healthcare provider for any questions regarding medication and dosages. Dosing may need to be adjusted based on specific patient factors, clinical context, and physician orders.
function calculateDose() {
var patientWeightKg = parseFloat(document.getElementById("patientWeightKg").value);
var drugDosagePerKg = parseFloat(document.getElementById("drugDosagePerKg").value);
var drugConcentrationUnit = document.getElementById("drugConcentrationUnit").value;
var drugConcentrationValue = parseFloat(document.getElementById("drugConcentrationValue").value);
var resultValueElement = document.getElementById("result-value");
var resultUnitElement = document.getElementById("result-unit");
// Clear previous results
resultValueElement.innerText = "–";
resultUnitElement.innerText = "";
// Validate inputs
if (isNaN(patientWeightKg) || patientWeightKg <= 0) {
alert("Please enter a valid patient weight (must be a positive number).");
return;
}
if (isNaN(drugDosagePerKg) || drugDosagePerKg <= 0) {
alert("Please enter a valid drug dosage per kg (must be a positive number).");
return;
}
if (isNaN(drugConcentrationValue) || drugConcentrationValue <= 0) {
alert("Please enter a valid drug concentration value (must be a positive number).");
return;
}
var totalDrugAmountMg;
var drugConcentrationMgPerMl;
// Convert concentration to mg/mL for consistent calculation
switch (drugConcentrationUnit) {
case "mg_per_ml":
drugConcentrationMgPerMl = drugConcentrationValue;
break;
case "mcg_per_ml":
drugConcentrationMgPerMl = drugConcentrationValue / 1000;
break;
case "g_per_ml":
drugConcentrationMgPerMl = drugConcentrationValue * 1000;
break;
default:
alert("Invalid concentration unit selected.");
return;
}
// Step 1: Calculate total drug amount needed in mg
totalDrugAmountMg = patientWeightKg * drugDosagePerKg;
// Step 2: Calculate volume to administer in mL
var volumeToAdministerMl = totalDrugAmountMg / drugConcentrationMgPerMl;
// Display the result
resultValueElement.innerText = volumeToAdministerMl.toFixed(2); // Display with 2 decimal places
resultUnitElement.innerText = "mL";
}