Drug Dose Rate Calculation Formula

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IV Drug Infusion Rate Calculator
mcg/kg/min (micrograms) mg/kg/min (milligrams) mcg/kg/hr mg/kg/hr mcg/min (Weight independent) mg/min (Weight independent) mg/hr (Weight independent)
mg (milligrams) mcg (micrograms) grams
Please enter valid positive numbers for all fields.
Infusion Flow Rate: 0.0 mL/hr
Calculated Concentration: 0 mcg/mL

About the Drug Dose Rate Formula

This calculator helps medical professionals, nurses, and pharmacy technicians calculate the correct IV infusion rate (flow rate) in milliliters per hour (mL/hr) based on a desired medication dosage. Accurate calculation of drug dose rates is critical in intensive care units (ICU), anesthesia, and emergency medicine to ensure patient safety.

The Core Formula

The calculation of an IV drip rate involves Dimensional Analysis to convert the desired dose (typically based on weight and time) into a volumetric flow rate. The general logic follows these steps:

Flow Rate (mL/hr) = [Total Dose Needed per Hour] ÷ [Concentration of Drug Solution]

When the dose is weight-based (e.g., mcg/kg/min), the expanded formula is:

Rate (mL/hr) = (Dose × Weight × 60) ÷ Concentration

Where:

  • Dose: The desired amount of drug per kilogram per minute (or hour).
  • Weight: Patient's body weight in kilograms (kg).
  • 60: Conversion factor (minutes to hours).
  • Concentration: Amount of drug per milliliter of solution (e.g., mcg/mL).

Common Unit Conversions

To ensure accuracy, all units must match before calculation. This calculator automatically handles these conversions:

  • 1 gram (g) = 1,000 milligrams (mg)
  • 1 milligram (mg) = 1,000 micrograms (mcg)
  • 1 hour = 60 minutes

Example Calculation

Scenario: A physician orders Dopamine at 5 mcg/kg/min for a patient weighing 70 kg. The pharmacy supplies a bag containing 400 mg of Dopamine in 250 mL of D5W.

  1. Calculate Concentration: 400 mg = 400,000 mcg.
    Concentration = 400,000 mcg ÷ 250 mL = 1,600 mcg/mL.
  2. Calculate Total Dose per Minute: 5 mcg × 70 kg = 350 mcg/min.
  3. Calculate mL per Minute: 350 mcg/min ÷ 1,600 mcg/mL = 0.21875 mL/min.
  4. Convert to Hourly Rate: 0.21875 mL/min × 60 min/hr = 13.1 mL/hr.

Disclaimer: This tool is for educational and verification purposes only. Always double-check calculations with approved hospital protocols and smart pump libraries before administering medication.

function calculateInfusionRate() { // 1. Get DOM elements var weightInput = document.getElementById('ddr_weight'); var doseInput = document.getElementById('ddr_dose'); var doseUnitSelect = document.getElementById('ddr_dose_unit'); var amountInput = document.getElementById('ddr_amount'); var amountUnitSelect = document.getElementById('ddr_amount_unit'); var volumeInput = document.getElementById('ddr_volume'); var resultBox = document.getElementById('ddr_result'); var flowRateSpan = document.getElementById('ddr_flow_rate'); var concSpan = document.getElementById('ddr_concentration'); var errorDiv = document.getElementById('ddr_error'); // 2. Parse Float Values var weight = parseFloat(weightInput.value); var dose = parseFloat(doseInput.value); var drugAmount = parseFloat(amountInput.value); var volume = parseFloat(volumeInput.value); // 3. Validation // Weight is optional if the unit is NOT weight-based, but we check logic below. // Basic check for required numbers: var doseUnit = doseUnitSelect.value; var isWeightBased = doseUnit.indexOf('_kg_') !== -1; if (isNaN(dose) || isNaN(drugAmount) || isNaN(volume) || volume <= 0 || drugAmount <= 0) { errorDiv.style.display = 'block'; resultBox.style.display = 'none'; return; } if (isWeightBased && (isNaN(weight) || weight <= 0)) { errorDiv.style.display = 'block'; errorDiv.innerText = "Please enter a valid weight for weight-based dosing."; resultBox.style.display = 'none'; return; } errorDiv.style.display = 'none'; // 4. Normalize Drug Amount to MICROGRAMS (mcg) // We use mcg as the base unit for calculation precision var drugAmountMcg = 0; var amountUnit = amountUnitSelect.value; if (amountUnit === 'g') { drugAmountMcg = drugAmount * 1000000; } else if (amountUnit === 'mg') { drugAmountMcg = drugAmount * 1000; } else { // mcg drugAmountMcg = drugAmount; } // 5. Calculate Concentration (mcg/mL) var concentrationMcgPerMl = drugAmountMcg / volume; // 6. Normalize Desired Dose to MICROGRAMS PER MINUTE (mcg/min) // Goal: Get total drug needed per minute regardless of weight var requiredMcgPerMin = 0; if (doseUnit === 'mcg_kg_min') { requiredMcgPerMin = dose * weight; } else if (doseUnit === 'mg_kg_min') { requiredMcgPerMin = (dose * 1000) * weight; } else if (doseUnit === 'mcg_kg_hr') { requiredMcgPerMin = (dose * weight) / 60; } else if (doseUnit === 'mg_kg_hr') { requiredMcgPerMin = ((dose * 1000) * weight) / 60; } else if (doseUnit === 'mcg_min') { requiredMcgPerMin = dose; } else if (doseUnit === 'mg_min') { requiredMcgPerMin = dose * 1000; } else if (doseUnit === 'mg_hr') { requiredMcgPerMin = (dose * 1000) / 60; } // 7. Calculate Flow Rate // Rate (mL/min) = Required (mcg/min) / Concentration (mcg/mL) var rateMlPerMin = requiredMcgPerMin / concentrationMcgPerMl; // Rate (mL/hr) = Rate (mL/min) * 60 var rateMlPerHr = rateMlPerMin * 60; // 8. Display Results // Rounding to 1 decimal place usually sufficient for IV pumps flowRateSpan.innerText = rateMlPerHr.toFixed(1); // Display calculated concentration for verification concSpan.innerText = concentrationMcgPerMl.toFixed(2); resultBox.style.display = 'block'; }

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