NUR1141: Pharmacology
Dosage Calculation II
Review Conversions
XX MCG
Review - Conversions
Household
1 oz. = 30 ml = 2 TBSP
1 tsp = 5 ml
1 cup = 8 oz
Grains
1 grain = 60 mg
(some reference others: 62mg – 65 mg)
Weight
Kg =2.2 lbs.
Divide lbs. by 2.2 to get the weight in kg
Multiply kilograms by 2.2 to get lbs.
Review – Dosage Calculation Formula
Sample Sliding Scale
Humulin R U-100 based on result of finger stick every 8 hours:
0–180 mg per dL……….No coverage
181–240 mg per dL…….2 units subq
241–300 mg per dL…….4 units subq
341–400 mg per dL…….4 units subq
Greater than 400 per dL…..8 units subq and call health care provider.
Repeat reading in 2 hours.
Insulin Label
Various Syringes for Insulin
Practice
Common IV Solutions
NaCl
NS
½ NS
D5W or 5% D/W
D5RL
RL or RLS
D5NS
D5 and ½ NS (0.45%)
Sodium chloride
Normal saline (0.9% NaCl)
½ Normal saline (0.45% NaCl)
Dextrose 5% in water
Dextrose 5% and lactated Ringer’s
Lactated Ringer’s solution (electrolytes)
Dextrose 5% in Normal saline (0.9% NaCl)
Dextrose 5% in ½ Normal saline (0.45% NaCl)
Calculating Rate in Milliliter per Hour
Ordered X Q = X ml/hr
Available
Example 1:
• A solution of labetelol (Trandate) 100 mg per 100 mL of D5W is to infuse at a
rate of 25 mg per hr. Calculate the rate to infuse the solution in mL per hr.
25 mg/hr X 100 ml = 25 ml/hr
100 mg
Practice
A solution of Isuprel 2 mg in 250 mL D5W is to infuse at a rate of 5
mcg/min. Round your answer to the nearest whole number.
Ordered X Q = X ml/hr
Available
Calculating Percentage of Solute in IV Fluids
• Solution strength in percentage = grams of solute in 100 mL of fluid
• Example: D5W or 5% dextrose in water = 5 g dextrose per 100 mL
• How many g of dextrose is in 500 ml
Calculating Flow Rates for Infusion Pumps
• Identify the following:
• Volume
• Time in hours
• Round flow rate to the nearest whole number or tenths depending on the
equipment (or instructions)
solution (mL) = X ml/hr
time (hr)
Practice
Client with an infusion pump has an order for 3,000 mL D5W over 24
hours. Pump is regulated in mL/hr.
Set up in formula:
solution (mL) = X ml/hr
time (hr)
3000 ml = 125 ml/hr
24 hours
Practice
• Dilute amikacin 400 mg in 100 mls of D5W and infuse over 30
minutes. What is the flow rate in ml/hr?
Set up in formula:
solution (mL) = X ml/hr
time (hr)
• Convert minutes to hours before putting into the formula
• Total minutes/60 minutes = hour
Calculating IV Flow Rates in Drops (gtt) per Minute
• If pumps are not available, the rate is manually regulated with flow
regulator in tubing.
• Drops per minute is determined by the drop factor (gtt/mL) of the
drip chamber below IV bag.
• Adjust gtt/min by placing a watch that has a second hand close to the
drip chamber and counting the drops.
• Remember answers in gtts must always be in whole numbers (Not
possible to measure a partial drop)
• Drop factor is printed on package; NEVER assume.
IV Tubing
• Macrodrop
• Standard type for general infusions
• Delivers 10, 15, or 20 gtt/mL for each mL
• Used to deliver large volumes
• Microdrop
• Delivers tiny drops—60 gtt/mL
• Used to deliver small amounts with precision
• Because there are 60 minutes in an hour, the number of microdrops per
minute is equal to the number of mL/hr. (e.g., 25 gtts/min = 25 ml/hr).
Formula Method/Flow Rate in gtt/min
amount of solution (mL) x (drop factor) = X gtts/min
Time in minutes
Practice
You must calculate the rate in gtt/min. You check the tubing package
and find a drop factor of 20 gtt/ml. You recall the order:
1 L NS IV at 100 mL/hr now
• What is the rate in gtt/min.?
amount of solution (mL) x (drop factor) = X gtts/min
Time in minutes
Practice
IV medication in 50 mL NS in 20 minutes. Drop factor: microdrop (60
gtt/mL). At what rate in gtt/min should the IV be regulated?
amount of solution (mL) x (drop factor) = X gtts/min
Time in minutes
Practice
Order: 1,500 mL 0.9% NS in 10 hr. Drop factor: 15 gtt/mL. At what rate
in gtt/min should the IV infuse?
Practice
• Order: Keflin 2 g IVPB (piggyback) over 30 min. The Keflin is placed in
100 mL of fluid after it is dissolved. The drop factor is 15 gtt/mL. At
what rate in gtt/min should the IV be regulated?
Practice
An IV is regulated at 20 microgtt/min. How many hours will it take for
100 mL to infuse?
 Because drop factor is a microgtt; drops per minute equals mL per
hour (e.g., 20 mL per hr = 20 gtt/min).
100 ml
20 ml/hr
= 5 hours
Heparin
• Heparin is available in different strengths; read labels carefully before
administering to ensure the client’s safety.
• Verify the dosage, vial, and amount to be given.
• Obtain independent verification of the dosage to ensure accuracy.
• Heparin is a high-alert medication and must be double-checked by another
nurse.
Heparin
Order: Heparin 7,500 units subQ daily
Available: Heparin labeled 10,000 units per mL
What will you administer to the client?
Ordered X Q = X
Available
7500 units X 1 ml = 0.75 ml
10000 units
Calculation of IV Heparin Solutions
Calculating Units per Hour
• Order: Infuse solution of 1 L D5W with 20,000 units of heparin at 30 mL per hour.
Calculate the dosage of heparin the client receives per hour.
Units
x
total solution/ml
ml = units/hr
hr
Calculating Milliliter per Hour From Units per Hour
• Because heparin should always be infused via electronic pumps, it is necessary to
calculate in mL per hr.
• Order: Infuse heparin 850 units per hr from a solution containing D5W 500 mL with
heparin 25,000 units IV.
Total solution/ml x units = ml/hr
Units
hr
Practice
Infuse 1,200 units of heparin per hour from a solution containing
20,000 units in 250 mL D5W
Total solution/ml x units = ml/hr
Units
hr
Units/kg Common Calculations
• How many mL will you administer as a bolus?
• Bolus = units/kg X kg =
• What will the infusion rate be in units/hr?
• Units/kg/hr X kg = units/hour
• What will the infusion rate be in ml/hr?
• Ordered/Available X Q = ml/hr
Practice
Mr. Flint weighs 165 lb. You have on hand 25,000 units in 1,000 mL of
0.9% sodium chloride. You review the order for Mr. Flint’s heparin drip.
Heparin bolus 80 units/kg then initiate drip at 18 units/kg/hr.
How many mL will you administer as a bolus?
Ordered Bolus amount = units/kg X kg = X units
What will the infusion rate be in units/hr?
Ordered Infusion = Units/kg/hr X kg = units/hr
What will the infusion rate be in ml/hr?
Ordered X Q = ml/hr
Available
Practice
A client weighs 154 lb. Heparin infusion 20,000 units in 1,000 mL 0.9%
sodium chloride. Order: Bolus with heparin sodium at 80 units/kg, then
initiate drip at 14 units/kg/hr.
Ordered Bolus amount = units/kg X kg = X units
Bolus dosage__________________________
Ordered Infusion = Units/kg/hr X kg = units/hr
Infusion rate __________________________
Ordered X Q = ml/hr
Available
ml/hr __________________________
Practice
• The prescriber orders Narcan 1.2 mg IV stat for a child who weighs 12
kg. You need to determine if the dosage is safe.
• Recommended dosage is 0.1 mg/kg/dose from a reputable
medication resource
• 0.1 mg X 12 kg = 1.2 mg is the recommended dose
• The physician ordered 1.2 mg
• The dose is safe for this child.
Practice
• The prescriber orders Vistaril 15 mg IM q4h prn for nausea. The child
weighs 38 lb. You need to determine if the dosage is safe.
• The recommended dosage is 0.5 to 1 mg/kg/dose q4h prn from a
reputable medication resource.
• Convert lbs to kg. 38 / 2.2 = 17.3 kg
• 0.5 mg x 17.3 kg = 8.65 round to 8.7 mg/dose
• 1 mg x 17.3 kg = 17.3 mg/dose
• The physician ordered 15 mg/dose
• This is a safe dosage.
Practice
• Order: Gentamicin 50 mg IVPB q8h for a child weighing 40 lb. The
recommended dosage for a child is 6 to 7.5 mg/kg/day divided q8h. Is
the dosage ordered safe?
• Convert 40 lbs to kg = 40/2.2 = 18.1818 round to 18.2 kg
• 6 mg x 18.2 kg = 109.2 mg/day
• 7.5 mg x 18.2 kg = 136.5 mg/day
• Physician ordered 50 mg q8h = 50 mg x 3 times per day = 150
mg/day
• No, this dose is not safe. It exceeds recommendations.
The physician ordered
amoxicillin 150 mg PO
every 8 hours
The child weights 36
pounds
1. How many kg does
the child weigh?
2. Is the prescribed
dosage within
parameters?
3. How many ml should
the child receive per
dose?