Paramedic Drug Calculations: Drip Rates, Weight-Based Dosing, and Conversions

Drug Calculation Fundamentals

Medication math is a critical paramedic skill tested on the NREMT. Errors in drug calculations can be fatal. Master these formulas and practice until calculations become automatic.

Basic Conversion Factors

• 1 g = 1,000 mg
• 1 mg = 1,000 mcg
• 1 kg = 2.2 lbs
• 1 L = 1,000 mL

Weight conversion: Patient weight in kg = weight in lbs / 2.2

Desired Over Have Formula

The most fundamental drug calculation formula:

Volume to administer = (Desired dose / Concentration on hand) x Volume on hand

Example: You need to give 5 mg of a drug that comes as 10 mg/mL. Volume = (5 mg / 10 mg) x 1 mL = 0.5 mL

Weight-Based Dosing

Dose = Weight (kg) x Dose per kg

Example: Pediatric epinephrine at 0.01 mg/kg for a 20 kg child. Dose = 20 x 0.01 = 0.2 mg

Then use desired over have to determine the volume: If epinephrine is 0.1 mg/mL (1:10,000), Volume = (0.2 / 0.1) x 1 = 2 mL

IV Drip Rate Calculations

mL/hr (for IV pumps)

mL/hr = (Total volume x 60) / Time in minutes

Or simply: mL/hr = Total volume / Time in hours

gtts/min (for manual IV sets)

gtts/min = (Volume in mL x Drop factor) / Time in minutes

Common drop factors: 10 gtts/mL (macro), 15 gtts/mL (macro), 60 gtts/mL (micro)

Medication Infusion Calculations

For continuous infusions dosed in mcg/kg/min or mcg/min:

Dopamine Example

Order: Dopamine 5 mcg/kg/min. Patient weighs 80 kg. Concentration: 800 mg in 500 mL (1,600 mcg/mL)

1. Calculate dose per minute: 5 mcg/kg/min x 80 kg = 400 mcg/min
2. Convert to mL/min: 400 mcg/min / 1,600 mcg/mL = 0.25 mL/min
3. Convert to mL/hr: 0.25 x 60 = 15 mL/hr
4. If using 60 gtts/mL set: 15 gtts/min

Epinephrine Infusion Example

Order: Epinephrine 4 mcg/min. Concentration: 1 mg in 250 mL (4 mcg/mL)

1. mL/min = 4 mcg/min / 4 mcg/mL = 1 mL/min
2. mL/hr = 1 x 60 = 60 mL/hr
3. Using 60 gtts/mL set: 60 gtts/min

Common Paramedic Drug Concentrations

• Epinephrine 1:10,000: 0.1 mg/mL (cardiac arrest, IV/IO use)
• Epinephrine 1:1,000: 1 mg/mL (anaphylaxis, IM use)
• Atropine: 0.1 mg/mL
• Amiodarone: 50 mg/mL
• Adenosine: 3 mg/mL
• Morphine: 10 mg/mL
• Naloxone: 0.4 mg/mL (IV) or 4 mg/0.1 mL (intranasal)

Practice Tips

The key to drug calculation accuracy is setting up the problem correctly, canceling units, and double-checking your math. Write out every step. Do not try to do calculations in your head during a stressful situation. Use dimensional analysis to verify that your units cancel correctly, leaving you with the units you need for the answer.