dosage calulations part 1

1

Dosage CalculationsPart 1

• TODAY WE WILL PROCEED WITH DOSAGE CALCULATIONS.

• THIS PART IS THE REAL NURSING STUFF!!!!

Dosage Variations

• Reconstitution of powered drugs; single and multi-strength

• Pediatric meds

• BSA

• IV formulas

• Heparin

• Critical care medications

2

Reconstitution of Powered Medications

• Solute

• Solvent

• Directions

1. Read label instructions

2. Add diluent

3. Label and calculate dose to administer

3

4

Reconstitution of Powdered Drugs

Example: Bottle of Oxacillin 2 g powder

Directions on label: add 11.5ccsterile H20 for injectionEach 1.5 cc = 250 mg

Dose ordered is 500mg IMHow many________ cc’s will we give?

250 mg: 1.5cc :: 500 mg : Xcc

250X = 500mg x 1.5250X= 750

X = 3cc

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

Single Dose ReconstitutionExample 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

Reconstitution cont.

• Don’t worry about the added amount, just use resulting concentration

( 500mg/ml)

• 500 mg : 1ml :: 750 mg : x ml500x = 750

x = 1.5 ml

So we would give 1.5ml for ordered dose.

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

Label Example

9

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

MEDICAL QUESTION OF THE DAY

• QUESTION:

• WHAT IS AN ELIXIR

12

MEDICAL HUMOR

• ANSWER:: WHAT A DOG DOES TO HIS MASTER.

• LOL

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

Pediatric Medications

15

Dosage Calculation3 Steps

1. Convert lbs. – kgs. divide by 2.2

2. Calculate daily dosage

3. Compare to recommended safe dose.

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

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

Pediatric DosageExample 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

Example 2Pediatric 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!

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

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

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

BSA(Body Surface Area)

Noted as M2

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

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

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

Example #2

• Child BSA = 0.6m²

• Recommended Adult dose of

• Keflex = 500 mg

• Find the child dose

29

ANSWER BSA

0.6 X 500 = 1.7 176.47 MG = CHILD

DOSE

30

NON-METRICBSA =

wt (lbs) x ht (in)3131

METRICBSA =

WT (kg) x ht (cm)3600

**May use to calculate adult or pediatric dose

31

AVERAGE 4YR OLD17KG and 103 CM

3600

10317x

3600

1751

49..486. or

.697m2 or 0.7m2

=

=

=

32

BSA

• Example 2

• Calculate the BSA for adult who weighs 200lbs and is 59”tall

33

ANSWER

Use non metric formula

BSA =

200x59

3131

= 3.768

Answer = 1.94 is the BSA

34

MEDICAL HUMOR

• QUESTION

• WHAT IS A MICROGRAM

35

MEDICAL HUMOR

• ANSWER :

• A SMALL CRACKER

• LOL again