Nursing Education
Calculating Drug Dosage
1. Ba s ic Ra tio & P ro p o rtio n Ca lc u la tio n
Wh e n th e d o s e o n h a n d is n o t th e s a m e a s th e d e s ire d p e r o rde re d d o s e
Dose on hand
Quantity on hand
===
Desired dose (Drug order)
Quantity desired (x )
=
For example: 500 mg is ordered. It is available in 250 mg capsule (s).
Solve X to get the number of capsule(s) to give
S te p 1
Dose on hand (250mg)
Quantity on hand (1 capsule)
===
Desired dose (500mg)
=
Quantity desired (x capsule(s))
S te p 2
250 mg
500mg
===
1 capsule
=
x capsule(s)
Resulting in an equation: 250mg x X capsule(s) = 1 capsule x 500mg
S te p 3
===
X capsule(s)
=
1 capsule x 500 mg
250 mg
=
S te p 4
An s we r:
JW 9/10, JW 2/13
2 Capsules
1
500
250
Nursing Education
Calculating Drug Dosage
Dose on hand
Quantity on hand
Desired dose (Drug order)
Quantity desired (x )
===
=
For example: 5000 units are ordered. It is available in a vial containing 10,000 units/mL.
Solve X to get the number of mL(s) to give
S te p 1
Dose on hand (10, 000 Units)
Quantity on hand (1 mL)
===
Desired dose (5000 units)
=
Quantity desired (x mL)
S te p 2
10,000 Units
1 mL
5000 Units
===
=
x mL
Resulting in an equation: 10,000 Units x X capsule(s) = 1 mL x 5000 Units
S te p 3
===
X capsule(s) =
1 mL x 5000 Units =
10, 000 Units
5000
10,000
S te p 4
An s we r:
JW 9/10, JW 2/13
0.5 mL
2
Nursing Education
Calculating Drug Dosage
2. Ca lc u la tin g Me d ic a tio n in S olu tion
Volume to be Administered
=
Dose Ordered
Available concentration in 1 mL
For example: 8 mg is ordered. It is available as 10mg/mL
S te p 1
Volume to be Administered
=
Dose Ordered (8 mg)
Available concentration in 1 mL (10 mg/mL)
S te p 2
8
10 mL
S te p 3
An s we r:
0.8 mL
*** If concentration is not available for 1 mL, you must calculate the concentration for 1 mL by
taking the total dose and dividing it by the total volume to calculate dose per mL
For example: Calculate the mg/mL concentration for 50 mg of a drug in 100 mL
S te p 1
50
100 mL
S te p 2
An s we r:
JW 9/10, JW 2/13
0.5 mg/mL
3
Nursing Education
Calculating Drug Dosage
3. Ca lc u la tin g IV Flow Ra te s
For example: 1000 mL IV solution ordered to infuse over 8 hours
S te p 1
1000 mL
8 hr
===
=
(x mL)
1 hr
Resulting in an equation: 8 hr x X mL = 1000 mL x 1 hr
S te p 2
X mL
1000 mL x 1 hr
8 hr
=
S te p 3
An s we r:
JW 9/10, JW 2/13
125 ml/hr
4
Nursing Education
Calculating Drug Dosage
4. Ca lc u la tin g a Drip Ra te u s in g a n IV Tu b in g Drip Fa c to r
Th e Drip Ra te is th e n u m b e r o f d ro p s (g tts ) p e r m in to b e in fu s e d (g tts /m in )
Th e Drip Fa c to r o f th e IV tu b in g is d e te rm in e d b y th e m a n u fa c tu re r. Th is in fo rm a tio n c a n b e
fo u n d o n th e IV tu b in g p a c ka g in g . Th e Drip Fa c to r is th e n u m b e r o f d ro p s th a t e q u a l 1 m L
o f s o lu tio n .
IV Drip Rate (gtts/min)
Volume to be Infused (mL) x Drip Factor of tubing (gtts/mL)
Time (in min) to be infused
=
For example: 1000 mL of NS ordered to be administered over 8 hours. The IV tubing drip factor is 10 gtts/mL.
S te p 1 : Co ve rt Ho u rs to Min u te s
The IV infusion is ordered to be administered over 8 hours
There are 60 minutes in 1 hour
8 hours x 60 minutes = 480 minutes
S te p 2
IV Drip Rate (gtts/min)
=
1000 mL x 10 (gtts/mL)
480 min
=
10000 gtts
480 min
S te p 3
IV Drip Rate (gtts/min)
S te p 4
An s we r:
20.83 gtts/min
Round to nearest whole number = 21 gtts/min
JW 9/10, JW 2/13
5