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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

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Reconstitution of Powered Medications

• Solute

• Solvent

• Directions

1. Read label instructions

2. Add diluent

3. Label and calculate dose to administer

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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

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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

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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.

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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

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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 ?

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MEDICAL QUESTION OF THE DAY

• QUESTION:

• WHAT IS AN ELIXIR

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MEDICAL HUMOR

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

• LOL

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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

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Pediatric Medications

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Dosage Calculation3 Steps

1. Convert lbs. – kgs. divide by 2.2

2. Calculate daily dosage

3. Compare to recommended safe dose.

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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

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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?

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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?

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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

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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

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BSA(Body Surface Area)

Noted as M2

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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

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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

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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

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Example #2

• Child BSA = 0.6m²

• Recommended Adult dose of

• Keflex = 500 mg

• Find the child dose

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ANSWER BSA

0.6 X 500 = 1.7 176.47 MG = CHILD

DOSE

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NON-METRICBSA =

wt (lbs) x ht (in)3131

METRICBSA =

WT (kg) x ht (cm)3600

**May use to calculate adult or pediatric dose

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AVERAGE 4YR OLD17KG and 103 CM

3600

10317x

3600

1751

49..486. or

.697m2 or 0.7m2

=

=

=

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BSA

• Example 2

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

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ANSWER

Use non metric formula

BSA =

200x59

3131

= 3.768

Answer = 1.94 is the BSA

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MEDICAL HUMOR

• QUESTION

• WHAT IS A MICROGRAM

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MEDICAL HUMOR

• ANSWER :

• A SMALL CRACKER

• LOL again