IV Medications¶
Overview¶
IV medications require an additional calculation step beyond standard fluid rates. You must calculate not only the flow rate but also the dose being delivered per unit of time — and verify it matches the order.
Types of IV Medication Orders¶
| Order Type | Example |
|---|---|
| Fixed dose over time | vancomycin 1000 mg over 60 min |
| Continuous infusion by rate | heparin 1000 units/hr |
| Weight-based continuous | dopamine 5 mcg/kg/min |
| Intermittent piggyback (IVPB) | metronidazole 500 mg over 30 min |
Concentration¶
IV medication concentrations are expressed as amount of drug per volume of fluid:
Example: 500 mg of drug mixed in 250 mL of fluid:
Fixed Dose Over Time¶
Example 1: Order: vancomycin 1000 mg in 250 mL over 90 minutes What is the flow rate in mL/hr?
Convert time to hours: [90 \text{ min} \times \frac{1 \text{ hr}}{60 \text{ min}} = 1.5 \text{ hr}]
Calculate rate: [\frac{250 \text{ mL}}{1.5 \text{ hr}} = 166.7 \text{ mL/hr}]
Round to: 167 mL/hr
Example 2: Order: metronidazole 500 mg in 100 mL over 30 minutes What is the flow rate in mL/hr?
Continuous Infusion by Dose Rate¶
When an order specifies a dose rate (units/hr, mg/hr), calculate the flow rate from the concentration.
Example 3: Order: heparin 1200 units/hr Stock: heparin 25,000 units in 500 mL 0.9% NaCl
Step 1 — find concentration: [\frac{25{,}000 \text{ units}}{500 \text{ mL}} = 50 \text{ units/mL}]
Step 2 — calculate flow rate: [\frac{1200 \text{ units/hr}}{50 \text{ units/mL}} = 24 \text{ mL/hr}]
Example 4: Order: morphine 2 mg/hr IV continuous Stock: morphine 50 mg in 250 mL 0.9% NaCl
Step 1 — concentration: [\frac{50 \text{ mg}}{250 \text{ mL}} = 0.2 \text{ mg/mL}]
Step 2 — flow rate: [\frac{2 \text{ mg/hr}}{0.2 \text{ mg/mL}} = 10 \text{ mL/hr}]
Weight-Based Continuous Infusions¶
Weight-based IV medications are ordered in mcg/kg/min or mcg/kg/hr.
Example 5: Order: dopamine 5 mcg/kg/min IV Patient weight: 70 kg Stock: dopamine 400 mg in 250 mL D5W
Step 1 — calculate dose per minute: [70 \cancel{\text{ kg}} \times \frac{5 \text{ mcg}}{1 \cancel{\text{ kg}} \cdot \text{min}} = 350 \text{ mcg/min}]
Step 2 — convert mcg/min to mg/hr: [350 \cancel{\text{ mcg/min}} \times \frac{1 \cancel{\text{ mg}}}{1000 \cancel{\text{ mcg}}} \times \frac{60 \text{ min}}{1 \text{ hr}} = 21 \text{ mg/hr}]
Step 3 — find concentration: [\frac{400 \text{ mg}}{250 \text{ mL}} = 1.6 \text{ mg/mL}]
Step 4 — calculate flow rate: [\frac{21 \text{ mg/hr}}{1.6 \text{ mg/mL}} = 13.125 \text{ mL/hr}]
Round to: 13 mL/hr
Verifying Dose from Rate¶
Sometimes you need to verify what dose a patient is receiving from a running infusion.
Example 6: An IV is running at 30 mL/hr. Stock: 500 mg in 250 mL What dose is the patient receiving per hour?
Step 1 — concentration: [\frac{500 \text{ mg}}{250 \text{ mL}} = 2 \text{ mg/mL}]
Step 2 — dose rate: [30 \text{ mL/hr} \times 2 \text{ mg/mL} = 60 \text{ mg/hr}]
High Alert IV Medications¶
High Alert IV Medications
The following IV medications require independent double checking of all calculations and pump settings:
- Heparin — risk of serious bleeding
- Insulin — risk of severe hypoglycemia
- Morphine and opioids — risk of respiratory depression
- Dopamine and vasopressors — risk of cardiovascular collapse
- Chemotherapy — risk of severe toxicity
- Concentrated electrolytes — risk of cardiac arrest
Never administer these medications without a verified independent double check.
Practice Problems¶
Problem 1
Order: ampicillin 500 mg in 100 mL over 30 minutes What is the flow rate in mL/hr?
Answer
Problem 2
Order: heparin 1500 units/hr IV Stock: 25,000 units in 500 mL 0.9% NaCl What is the flow rate in mL/hr?
Answer
Concentration: [\frac{25{,}000 \text{ units}}{500 \text{ mL}} = 50 \text{ units/mL}]
Flow rate: [\frac{1500 \text{ units/hr}}{50 \text{ units/mL}} = 30 \text{ mL/hr}]
Problem 3
Order: morphine 3 mg/hr IV continuous Stock: morphine 50 mg in 500 mL 0.9% NaCl What is the flow rate in mL/hr?
Answer
Concentration: [\frac{50 \text{ mg}}{500 \text{ mL}} = 0.1 \text{ mg/mL}]
Flow rate: [\frac{3 \text{ mg/hr}}{0.1 \text{ mg/mL}} = 30 \text{ mL/hr}]
Problem 4
Order: vancomycin 1500 mg in 500 mL over 3 hours What is the flow rate in mL/hr?
Answer
Round to: 167 mL/hr
Problem 5
Order: dopamine 3 mcg/kg/min IV Patient weight: 80 kg Stock: dopamine 400 mg in 250 mL D5W What is the flow rate in mL/hr?
Answer
Step 1 — dose per minute: [80 \cancel{\text{ kg}} \times \frac{3 \text{ mcg}}{1 \cancel{\text{ kg}} \cdot \text{min}} = 240 \text{ mcg/min}]
Step 2 — convert to mg/hr: [240 \cancel{\text{ mcg/min}} \times \frac{1 \cancel{\text{ mg}}}{1000 \cancel{\text{ mcg}}} \times \frac{60 \text{ min}}{1 \text{ hr}} = 14.4 \text{ mg/hr}]
Step 3 — concentration: [\frac{400 \text{ mg}}{250 \text{ mL}} = 1.6 \text{ mg/mL}]
Step 4 — flow rate: [\frac{14.4 \text{ mg/hr}}{1.6 \text{ mg/mL}} = 9 \text{ mL/hr}]
Problem 6
An IV is running at 20 mL/hr. Stock: heparin 25,000 units in 500 mL What dose of heparin is the patient receiving per hour?
Answer
Concentration: [\frac{25{,}000 \text{ units}}{500 \text{ mL}} = 50 \text{ units/mL}]
Dose rate: [20 \text{ mL/hr} \times 50 \text{ units/mL} = 1000 \text{ units/hr}]
Clinical Tip
When hanging a new IV medication always perform a three-way check:
- Verify the drug name and concentration on the bag matches the order
- Verify the pump rate matches your calculation
- Verify the patient using two identifiers before connecting the line
These three checks take less than 60 seconds and prevent the most common IV medication errors.