1. 1
Dosage Calculations
Part 1
• TODAY WE WILL PROCEED WITH
DOSAGE CALCULATIONS.
• THIS PART IS THE REAL NURSING
STUFF!!!!

2. Dosage Variations
• Reconstitution of powered drugs; single and
multi-strength
• Pediatric meds
• BSA
• IV formulas
• Heparin
• Critical care medications
2

3. Reconstitution of Powered Medications
• Solute
• Solvent
• Directions
1. Read label
instructions
2. Add diluent
3. Label and calculate
dose to administer
3

4. 4
Reconstitution of Powdered Drugs
Example: Bottle of Oxacillin 2 g powder
Directions on label: add 11.5cc
sterile H20 for injection
Each 1.5 cc = 250 mg
Dose ordered is 500mg IM
How many________ cc’s will we give?
250 mg: 1.5cc :: 500 mg : Xcc
250X = 500mg x 1.5
250X= 750
X = 3cc

5. Reconstituting Medications
• For Calculating Purposes:
• DO NOT USE the added diluent for calculating your
dose. (see previous example)
• INSTEAD USE THE RESULTING
CONCENTRATION, e.g. in the previous example it
said the resulting concentration will be, 250mg =
1.5 ml
5

6. 6
Single Dose Reconstitution
Example 2
Order reads
• Give 750mg of Ampicillin q4h IV.
On hand
• Ampicillin 1 g vial in powered form.
• Reconstitution directions say:
add 2ml sterile water for injection. Each ml contains
500mg Ampicillin.
How many ml would you give each dose

7. 7
Reconstitution cont.
• Don’t worry about the added
amount, just use resulting concentration
( 500mg/ml)
• 500 mg : 1ml :: 750 mg : x ml
500x = 750
x = 1.5 ml
So we would give 1.5ml for ordered dose.

8. 8
Multiple Strength Solutions
Order reads
Penicillin G 2,250,000 units IM now.
ON Hand
Penicillin 20 million unit vial
Reconstitution reads:
• Add 11.5cc for 1,000,000 units/ml, 33cc for 500,000
units/ml, and 75cc for 250,000 units/ml
• Using the appropriate concentration, how many cc’s
should be given for this dose

9. Label Example
9

10. 10
Multiple Strength cont.
• Choose 1,000,000 units/ml
• since it is the closest. SO,
1,000,000units :1cc :: 2,250,000units : x cc
1,000,000 x = 2,250,000
x = 2.25cc
• So give 2.25 cc to administer dose.
• Ok for IM
Injection ?

11. 11
MEDICAL QUESTION OF THE DAY
• QUESTION:
• WHAT IS AN ELIXIR

12. 12
MEDICAL HUMOR
• ANSWER:: WHAT A DOG DOES TO
HIS MASTER.
• LOL 

13. 13
DOSAGE CALCUATION
BY WEIGHT
ORDER:Vancomycin IV 5 mg/kg
Patient weights 209 lbs
209 ÷ 2.2 = 95 kg
95 kg X 5 mg = 475 mg

14. 14
Pediatric Medications

15. 15
Dosage Calculation
3 Steps
1. Convert lbs. – kgs. divide by 2.2
2. Calculate daily dosage
3. Compare to recommended safe dose.

16. 16
Order: Amoxicillin 125 mg
P.O. q.8
***Patient weight 22 lbs
IS THIS DOSE SAFE?
STEPS:
1. 22 ÷ 2.2 = 10 kg
2. 125mg q 8hr. = 125 mg x 3
24 hrs ÷q 8 hrs. = 3 x /day
= 375 mg per day

17. 17

18. 18
Pediatric Dosage
3. Recommended safe dose of Amoxicillin is
20-40 mg/kg/day.
20mg x 10kg = 200mg /day
40 mg x 10 kg = 400mg /day
So daily safe range is
200mg – 400mg /day
Patient’s daily dose is 375 mg/day
So patient’s daily dose falls within SAFE range

19. Pediatric Dosage
Example 2
• Order reads: Oxycodone 3mg p.o. now
• Patient weighs 30 lbs.
• Recommended safe dose of Oxycodone is
0.15 mg/kg/dose
Is this dose safe?
19

20. 20
Example 2
Pediatric dosage
1. 30 lbs / 2.2 = 13.64 kg.
2. Ordered dose is 3 mg.
3. Recommended dose is 0.15 mg/kg/dose
0.15 x 13.64 = 2 mg is the maximum safe
dose
This dose is not safe!

21. Example 3
• Order reads: Gentamycin 5mg/kg/day divided in
2 doses.
• The infant weighs
• 22lbs.
• On hand is: Gentamycin 80mg/2ml
• How many cc’s should the infant receive per
dose?
21

22. Example 3 (cont.)
• Infant weight in kg = 22/2.2 or 10 kg
• 5mg x 10mg = 50 mg /day in 2 divided doses =
25 mg per dose
• On hand we have Gentamycin
80mg/2ml
SO, 80mg : 2ml :: 25 mg: xml
80x = 50
x = 0.625ml per dose
22

23. 23
DOSAGE SAFETY
• A TRAGIC MEDICATION
ERROR LED TO DEATH OF 9- MONTH OLD INFANT.
THE DR. ORDERED .5mg IV MSO4
THE person who transcribed med DID NOT SEE THE DECIMAL MADE IT
A (5 mg)
DOSE ON MAR. (Medicine administration record)
BABY received 2 (5mg) DOSES
TWO HOURS APART.
THIS IS 10 TIMES THE NORMAL DOSE TWICE!! BABY DIED!!
New System POE many safety features !! Electronic records
improving safety

24. 24
BSA
(Body Surface Area)
Noted as M2

25. 25
Example
** If you are given a recommended pediatric dose
and BSA, use this formula**
Drug A : 15 mg/M2
(Recommended Pediatric Dose)
Pts. BSA = 0.48 M2
Just multiply
Dosage: 15 x 0.48(BSA) =
7.2 mg

26. 26
Recommended Adult
Dose Only
Formula on sheet
IF NO RECOMMENDED CHILD DOSE
IS AVAILABLE USE
Child’s BSA X (times)
1.7 M² adult dose
(average adult BSA)
WILL GIVE YOU CHILD’S DOSE

27. 27
Example with no recommended
pediatric dose given
DRUG C = 25 mg
( RECOMMENDED ADULT
DOSE OF DRUG)
CHILD’S BSA = 0.47 M ²
0.47 M ² X 25 mg = 7 mg
1.7 M ² CHILD’S
DOSE

28. 28
Example #2
• Child BSA = 0.6m²
• Recommended Adult dose of
• Keflex = 500 mg
• Find the child dose

29. 29
ANSWER BSA
0.6 X 500 =
1.7
176.47 MG = CHILD
DOSE

30. 30
NON-METRIC
BSA =
wt (lbs) x ht (in)
3131
METRIC
BSA =
WT (kg) x ht (cm)
3600
**May use to calculate adult or
pediatric dose

31. 31
AVERAGE 4YR OLD
17KG and 103 CM
3600
10317x
3600
1751
49..486. or
.697m2
or 0.7m2
=
=
=

32. 32
BSA
• Example 2
• Calculate the BSA for adult who
weighs 200lbs and is 59”tall

33. 33
ANSWER
Use non metric formula
BSA =
200x59
3131
= 3.768
Answer = 1.94 is the BSA

34. 34
MEDICAL HUMOR
• QUESTION
• WHAT IS A MICROGRAM

35. 35
MEDICAL HUMOR
• ANSWER :
• A SMALL CRACKER
• LOL again 