Dosage calulations part 1
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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