Drug Infusion Rate Calculator

Calculate IV flow rates based on patient weight and dosage.

Medical Disclaimer: This tool is for educational purposes only. Always verify calculations with approved medical protocols and double-check with a pharmacist or second practitioner before administration.

Understanding Drug Infusion Calculations

In critical care and emergency medicine, precise administration of medication is vital. Many potent drugs, such as vasoactive agents (e.g., Dopamine, Norepinephrine) or antiarrhythmics, are dosed based on the patient's body weight and time. The Drug Infusion Rate Calculator helps clinicians convert a prescribed weight-based dose (mcg/kg/min) into a practical pump setting (mL/hr) or gravity drip rate (gtt/min).

How the Calculation Works

To determine the flow rate for an IV pump, three main variables are reconciled: the concentration of the medication in the solution, the patient's weight, and the desired dose per minute.

1. Calculate Concentration

First, we determine how much drug is in every milliliter of fluid. Since doses are often in micrograms (mcg) and supply is in milligrams (mg), a conversion is necessary (1 mg = 1000 mcg).

Formula: (Total Drug mg × 1000) / Total Volume mL = Concentration (mcg/mL)

2. Calculate Total Dose Per Minute

Next, we determine the total amount of drug the patient needs every minute based on their weight.

Formula: Prescribed Dose (mcg/kg/min) × Patient Weight (kg) = Total Dose (mcg/min)

3. Calculate Flow Rate (mL/hr)

Finally, we calculate how many milliliters of the solution are required to deliver that total dose. Since infusion pumps run in milliliters per hour, we multiply the minute rate by 60.

Formula: (Total Dose mcg/min / Concentration mcg/mL) × 60 min/hr = Flow Rate (mL/hr)

Example Scenario

Consider a patient weighing 80 kg who requires Dopamine at 5 mcg/kg/min. The pharmacy sends a bag containing 400 mg of Dopamine in 250 mL of D5W.

• Concentration: (400 mg × 1000) / 250 mL = 1,600 mcg/mL.
• Required Dose: 5 mcg/kg/min × 80 kg = 400 mcg/min.
• Flow Rate (mL/min): 400 mcg / 1,600 mcg/mL = 0.25 mL/min.
• Pump Setting: 0.25 mL/min × 60 = 15 mL/hr.

Drop Factors and Gravity Drips

If an electronic infusion pump is not available, manual flow control via a drip chamber is used. The tubing packaging specifies the "drop factor" (gtt/mL), which indicates how many drops equal one milliliter.

• Microdrip: Standard is 60 gtt/mL. Used for pediatric or precise medication administration.
• Macrodrip: Common sizes are 10, 15, or 20 gtt/mL. Used for rapid fluid resuscitation or general hydration.

The formula for drip rate is: (Flow Rate in mL/hr × Drop Factor) / 60 = Drops per Minute (gtt/min).