Clinical Calculations
Justin Cornewell, PharmD
About Me
● 2016 Manchester Graduate
● Pharmacy technician at Parkview Health from (2007-2016)
● Clinical-Staff Pharmacist at IU Health Ball Memorial Hospital (2016-present)
● PRN Floating Pharmacist at CVS Health (2016-present)
Purpose
● Provide a foundation to help facilitate discussion on rotations
● Understand why calculations are important
● Understand common errors made
● Establish “red flags”
● Recognize YOUR strengths and weaknesses
Process
Evaluate 04 01 Who
Calculation
03 02
How What
Objectives
1. Using a hospital protocol, accurately calculate the following:
a. Vancomycin dosing
b. Aminoglycoside dosing
2. Using a hospital protocol, optimize a patient’s medication based on renal function
3. Using a hospital protocol, initiate a TPN and make adjustments based on labs
4. Calculate a patient’s corrected calcium
5. Convert a patient opioid regimen to an alternative equivalent
6. Using a hospital protocol, calculate the rate in mL/hr of 3% sodium chloride to correct a patient’s
sodium level.
7. Calculate a patient’s body surface area
8. Calculate a patient’s etoposide dose
9. Calculate a carboplatin dose using the Calvert Equation
Materials Posted on Canvas
● Clinical Calculations presentation
● Clinical Calculations worksheet
● Formula sheet 1 and 2
● Pharmacokinetic Protocol
● Adult Medication Dosing Optimization Protocol
● Total Parenteral Nutrition Order Set
● Sodium Chloride 3%-BMH
● Small Cell Lung Cancer Carboplatin/Etoposide
● NCCN Carboplatin Dosing Guide
Format
● Workshop
○ Work independently on calculations
○ Check calculations with neighbors
● Ask questions
● Plan 5-10 min per calculation
● Review each calculation as a group
Vancomycin Dosing
***Refer to: Pharmacokinetic Protocol***
Objective 1a
Body Mass Index (BMI)
● Formula
○ BMI= weight (kg)/[height (m)]2
○ BMI= weight (pounds)/ ([height (inches)]2 x 703)
● Interpretation for Adults
BMI Weight Status
Below 18.5 Underweight
18.5-24.9 Normal or healthy weight
25-29.9 Overweight
30 and above Obese
Dosing Weight
● Ideal body weight (IBW)
○ Female: 45.5 kg + (2.3 x height over 5 feet in inches)
○ Male: 50 kg + (2.3 x height over 5 feet in inches)
● Adjusted body weight
○ IBW+0.4 (Actual body weight-IBW)
Renal Function
● AKI vs CKD
● SCr
● Urine output
● Nephrotoxic medications
AKI vs CKD
● AKI
○ Increase in SCr ≥0.3 mg/dL within 48 hours
○ Increase in SCr 1.5x baseline within past 7 days
○ Urine volume less than 0.5 mL/kg/hour for at least 6 hours
● CKD
○ Abnormal kidney function or structure for 3 months or greater
■ Persistent markers of kidney damage
■ GFR < 60 mL/min/1.73m2
Vancomycin Protocol
● Loading dose
○ Critically ill patients
○ Suspected or confirmed deep seated infections
■ Meningitis
■ Osteomyelitis
■ Endocarditis
○ 20-25 mg/kg
○ Max dose 2000 mg
○ Actual body weight vs adjusted body weight
Vancomycin Protocol
● Maintenance dose
○ Age
○ Renal function
○ Dosing weight
● Monitoring
○ Drawn 30-60 min before dose
○ DO NOT draw within first 3 days
■ Unless suspected nephrotoxicity
○ Drawn after 3rd day or 4th dose (if Q24H)
Dose Optimization
Refer to: Adult Dosing Optimization Protocol
Objective 2
Dosing Optimization Protocol
● Creatinine clearance
● Indication
● Pharmacist may adjust dose per P and T policy
● Extended infusions
○ Aztreonam
○ Piperacillin/tazobactam
○ Meropenem
○ Cefepime
Worksheet GT
● Ideal body weight:
● Adjusted body weight:
● Dosing weight:
● CrCl:
● Vancomycin dosing regimen:
● Piperacillin/tazobactam regimen:
Worksheet JC
● Ideal body weight:
● Adjusted body weight:
● Dosing weight:
● CrCl:
● Vancomycin dosing regimen:
● Trough level:
Aminoglycoside Dosing
***Refer to: Pharmacokinetic Protocol***
Objective 1b
Aminoglycoside Dosing
● Conventional dosing
○ Dosing depends on indication
● Extended interval dosing
○ Gentamicin/tobramycin 7 mg/kg
○ Amikacin 15 mg/kg
○ Preferred method for suspected or confirmed gram negative infection
○ Nomogram
Worksheet JS
● BMI:
● Dosing Weight:
● Creatinine Clearance:
● Gentamicin dosing regimen:
● Time to draw gentamicin level:
● Gentamicin dosing interval:
Opioid Calculations
Objective 3
Opioids
● Class Medications
Morphine-like Morphine, codeine, hydrocodone,
(phenanthrenes) hydromorphone, oxycodone, oxymorphone
Meperidine-like Meperidine, fentanyl
(phenylpiperidines)
Methadone Methadone
(diphenylheptane)
Central analgesics Tapentadol, tramadol
Opioid Conversions
Medication IV/IM (mg) Oral (mg)
Morphine 10 30
Hydromorphone 1.5 7.5
Oxycodone - 20
Hydrocodone - 30
Codeine 130 200
Fentanyl 0.1
Meperidine 75 300
Oxymorphone 1 10
Opioid Conversion Process
1. Calculate total 24 hour dose requirement
2. Use ratio-conversion to calculate dose of new drug
3. Calculate 24 hour dose of new drug
a. Reduce dose by at least 25%
4. Divide to attain appropriate interval and dose for new drug
5. Example:
30 mg of morphine PO x mg morphine PO
_____________________ = ____________________
1.5 mg IV hydromorphone 12 mg of IV hydromorphone
Opioid Conversion Example
Example:
A hospice patient has been receiving 12 mg of IV hydromorphone. Convert to
morphine ER. Hospital protocol states to reduce dose of new opioid by 50%.
30 mg of morphine PO x mg morphine PO
_____________________ = ____________________
1.5 mg IV hydromorphone 12 mg of IV hydromorphone
Worksheet AC
● 35 mg of hydromorphone IV is equivalent to ______ mg of morphine IV
● 35 mg of hydromorphone IV is equivalent to ______mcg of fentanyl IV
● What dosing regimen of fentanyl would you recommend to control the pain?
Worksheet AJ
● Morphine 24 mg IV is equivalent to _____ mg of morphine PO
● Morphine ______ mg PO is equivalent to ______mg of oxycodone PO
● What treatment regimen would you recommend?
Parenteral Nutrition
***Refer to: Total Parenteral Nutrition Order Set***
Objectives 3 & 4
Parenteral Nutrition
● Calories
○ 25-30 kcal/kg/day
○ IF BMI > 30
■ 22-25 kcal/kg/day based on IBW
● Protein
○ 4 kcal/g
○ 0.8-2 kcal/kg/day
● Lipids
○ 20-30% of kcals
● Carbohydrates
○ 3.4 kcal/g
Parenteral Nutrition
Parenteral Nutrition Formulas
Dextrose monohydrate 3.4 kcal/g
IVFE 10% 1.1 kcal/mL
IVFE 20 % 2 kcal/mL
IVFE 30% 3 kcal/mL
Amino acid solutions 4 kcal/g
Parenteral Nutrition (PN) Protocol
● Dietary and Pharmacy collaboratively write TPN’s at BMH
○ Dietician manages macronutrients
○ Pharmacy manages micronutrients
■ Can order electrolyte replacement
■ Can order labs
■ Orders the TPN
● All TPN orders must be received by 1600
Worksheet MC
● Corrected Calcium
● Calories from amino acids and how many mL assuming a 15% amino acid solution
● Calories from dextrose and how many mL assuming a 70% dextrose solution
● Calories from lipids and how many mL of lipids using a 10% formula
● Calculate the sum of calcium and phosphate (units must be normalized). HINT: 2
mEq/mmol of phosphate
Hyponatremia
Refer to: Sodium Chloride 3%-BMH
Objective 5
Sodium Chloride 3%-BMH
● Calculate the following
○ How many mEq of Na are in 500 mL of 3% NaCl?
○ Calculate the rate of 3% NaCl in mL/hr______________
○ Calculate the rate of 3% NaCl in mL/hr______________
Cancer Center Calculations
Refer to: Small Cell Lung Cancer
Carboplatin/Etoposide
Objectives: 6-9
Small Cell Lung Cancer Carboplatin/Etoposide
● Carboplatin
○ GFR estimated using Cockroft-Gault
■ MAX of 125 mL/min
■ If SCr is less than 0.7 mg/dL then round to 0.7 mg/dL
○ Calvert Formula
■ Carboplatin dose=AUC x (GFR +25)
○ NCCN carboplatin dosing guide
● Etoposide
○ Calculate BSA (Dubois-Dubois)
○ 100 mg/m2
JD-Carboplatin
● Carboplatin dose:
● Amount of carboplatin to be drawn up to compound (10 mg/mL
concentration):
● What size bag of NS to mix carboplatin in?
● Final Concentration:
JD-Etoposide
● Etoposide dose:
● Amount of etoposide to be drawn up to compound (20 mg/mL concentration):
● What size bag of NS to mix etoposide in?
● Final Concentration:
Wrapping Up
● Personal stories
● Rotations
○ Advice
● Life after pharmacy school
○ Community Pharmacy
○ Industry
○ Inpatient Pharmacy
○ Residency
■ PGY-1
■ PGY-2
Looking Ahead
● April 25th
○ Community pharmacy calculations
○ Inpatient pharmacy calculations
● Workshop format
Questions
● What questions do you have?
