Drug Calculations for Nurses
Accurate drug calculation is a cornerstone of safe nursing practice. Errors in medication administration can have serious, even fatal, consequences for patients. This tool provides two essential calculators to assist nurses in verifying medication dosages and infusion rates, helping to ensure patient safety and effective treatment.
Always double-check your calculations with another qualified professional and refer to your institution's policies and procedures. This calculator is a supplementary tool and does not replace critical thinking or professional judgment.
1. Dosage Volume from Concentration
Use this calculator to determine the exact volume (in milliliters) of a medication you need to administer, given the desired dose and the available concentration of the drug.
Desired Dose:
mg
mcg
units
g
Available Drug Concentration:
mg
mcg
units
g
/
mL
tablet
Calculate Volume
Result:
Volume to Administer: — mL
Example:
A physician orders 500 mg of a medication. The medication is available in a concentration of 250 mg/mL .
Calculation: 500 mg / 250 mg/mL = 2 mL
You would administer 2 mL of the medication.
2. IV Infusion Rate & Drip Rate
This calculator helps determine the infusion rate for an IV pump (mL/hr) and the manual drip rate (gtts/min) for gravity infusions, based on the total volume of the solution and the desired infusion time.
Total Volume of IV Solution (mL):
Infusion Time (hours):
Drop Factor of IV Tubing (gtts/mL):
Calculate IV Rates
Result:
Infusion Rate: — mL/hr
Drip Rate: — gtts/min
Example:
An IV solution of 500 mL needs to be infused over 4 hours . The IV tubing has a drop factor of 15 gtts/mL .
Calculation for Infusion Rate (mL/hr): 500 mL / 4 hours = 125 mL/hr
Calculation for Drip Rate (gtts/min): (500 mL * 15 gtts/mL) / (4 hours * 60 min/hour) = 7500 / 240 = 31.25 gtts/min
The IV pump should be set to 125 mL/hr , and the manual drip rate would be approximately 31 gtts/min .
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function calculateDosageVolume() {
var desiredDose = parseFloat(document.getElementById('desiredDose').value);
var desiredDoseUnit = document.getElementById('desiredDoseUnit').value;
var availableConcentration = parseFloat(document.getElementById('availableConcentration').value);
var availableConcentrationUnitNumerator = document.getElementById('availableConcentrationUnitNumerator').value;
var availableConcentrationUnitDenominator = document.getElementById('availableConcentrationUnitDenominator').value;
var resultDiv = document.getElementById('dosageVolumeResult');
var volumeToAdministerSpan = document.getElementById('volumeToAdminister');
if (isNaN(desiredDose) || isNaN(availableConcentration) || desiredDose <= 0 || availableConcentration <= 0) {
volumeToAdministerSpan.textContent = 'Invalid Input';
resultDiv.style.backgroundColor = '#ffe0e0';
resultDiv.style.borderColor = '#ffb3b3';
return;
}
// Unit conversion logic (simplified for common cases)
// For now, assume units match or are compatible (e.g., mg to mg, mcg to mcg)
// A more robust calculator would handle g to mg, mg to mcg conversions.
// For this example, we'll just check if the units are compatible for division.
if (desiredDoseUnit !== availableConcentrationUnitNumerator) {
volumeToAdministerSpan.textContent = 'Unit Mismatch';
resultDiv.style.backgroundColor = '#ffe0e0';
resultDiv.style.borderColor = '#ffb3b3';
return;
}
var volume = desiredDose / availableConcentration;
volumeToAdministerSpan.textContent = volume.toFixed(2); // Round to 2 decimal places
resultDiv.style.backgroundColor = '#e9f7ff';
resultDiv.style.borderColor = '#b3e0ff';
}
function calculateIVRates() {
var totalVolumeIV = parseFloat(document.getElementById('totalVolumeIV').value);
var infusionTimeHours = parseFloat(document.getElementById('infusionTimeHours').value);
var dropFactor = parseFloat(document.getElementById('dropFactor').value);
var resultDiv = document.getElementById('ivRatesResult');
var infusionRate_mL_hr_span = document.getElementById('infusionRate_mL_hr');
var dripRate_gtts_min_span = document.getElementById('dripRate_gtts_min');
if (isNaN(totalVolumeIV) || isNaN(infusionTimeHours) || isNaN(dropFactor) ||
totalVolumeIV <= 0 || infusionTimeHours <= 0 || dropFactor <= 0) {
infusionRate_mL_hr_span.textContent = 'Invalid Input';
dripRate_gtts_min_span.textContent = 'Invalid Input';
resultDiv.style.backgroundColor = '#ffe0e0';
resultDiv.style.borderColor = '#ffb3b3';
return;
}
var infusionRate_mL_hr = totalVolumeIV / infusionTimeHours;
var dripRate_gtts_min = (totalVolumeIV * dropFactor) / (infusionTimeHours * 60);
infusionRate_mL_hr_span.textContent = infusionRate_mL_hr.toFixed(1); // Round to 1 decimal place
dripRate_gtts_min_span.textContent = Math.round(dripRate_gtts_min); // Round to nearest whole number for drops
resultDiv.style.backgroundColor = '#e9f7ff';
resultDiv.style.borderColor = '#b3e0ff';
}