Calculating Flow Rates for Intravenous Medications
Intravenous Piggyback Infusions
Patients can receive a medication through a port in an existing IV line – this is called intravenous
piggyback (IVPB). Th secondary bag is usually higher than the primary bag so that the pressure in the
secondary line will be greater than the primary line. Therefore, the secondary medication infuses first.
A typical IVPB order might read:
cimetidine 300 mg IVPB q6h in 50 mL NS infuse over 30 min.
This is an order for IV piggyback infusion in which 300 mg of the drug cimetidine is diluted in 50 mL of a
normal saline solution must infuse in 30 minutes. So, the patient receives 300 mg of cimetidine in 30
minutes via a secondary line, and this dose is repeated every 6 hours.
, Example 1
The prescriber ordered: Ancef 1 g IVPB q4h
The package insert information is as follows: Add 50 ml sterile water to the bag of Ancef 1 g and infuse
in 30 minutes.
The tubing is labeled 20 drops per milliliter.
Calculate the flow rate in drops per minute for this antibiotic.
Step 1: Start with the given information
Given flow rate: 50 mL in 30 minutes = 50 mL/30 min
Known equivalences: 20 gtt/mL (drop factor)
Flow rate you want to find: ?gtt/min
Step 2: Calculate
50 mL 20 gtt gtt
30 min
X 1mL
= 33.3 min
So, the flow rate is 33 drops per minute
Intravenous Piggyback Infusions
Patients can receive a medication through a port in an existing IV line – this is called intravenous
piggyback (IVPB). Th secondary bag is usually higher than the primary bag so that the pressure in the
secondary line will be greater than the primary line. Therefore, the secondary medication infuses first.
A typical IVPB order might read:
cimetidine 300 mg IVPB q6h in 50 mL NS infuse over 30 min.
This is an order for IV piggyback infusion in which 300 mg of the drug cimetidine is diluted in 50 mL of a
normal saline solution must infuse in 30 minutes. So, the patient receives 300 mg of cimetidine in 30
minutes via a secondary line, and this dose is repeated every 6 hours.
, Example 1
The prescriber ordered: Ancef 1 g IVPB q4h
The package insert information is as follows: Add 50 ml sterile water to the bag of Ancef 1 g and infuse
in 30 minutes.
The tubing is labeled 20 drops per milliliter.
Calculate the flow rate in drops per minute for this antibiotic.
Step 1: Start with the given information
Given flow rate: 50 mL in 30 minutes = 50 mL/30 min
Known equivalences: 20 gtt/mL (drop factor)
Flow rate you want to find: ?gtt/min
Step 2: Calculate
50 mL 20 gtt gtt
30 min
X 1mL
= 33.3 min
So, the flow rate is 33 drops per minute
