2023 RxPrep Ch. 12 Clinical Calculations

BMI

Kg/m^2

BMI classifications*

Underweight:

Normal weight:

Overweight:

Obese:

Underweight: < 18.5

Normal weight: 18.5 - 24.9

Overweight: 25- 29.9

Obese: ≥ 30

IBW

male

50 + 2.3(inches over 60)

IBW

female

45.5 + 2.3(inches over 60)

AdjBW

IBW + 0.4(TBW-IBW)

When obese, IBW is used for dosing of the following medications:

- Aminophylline

- Theophylline

- Acyclovir

- Thyroxine

When obese, TBW is used for dosing of the following medications:

- LMWHs

- UFH

- Vancomycine

When obese, AdjBW is used for dosing of the following medications: is used for dosing of the following medications:

Aminoglycosides

Flow rate calculation

Use dimensional analysis to convert between units until only the required units remain

Cockcroft-Gault equation for CrCl

(140 - age)/(72 * Scr) x kg weight x (0.85 if female)

Cockcroft-Gault equation

In what scenario would use the following weights to calculate CrCl?

- TBW

- IBW

- AdjBW

- TBW : if pt is underweight

- IBW : if IBW is ~ TBW

- AdjBW : Overweight > 25 BMI

A BUN:Scr ratio > ____ : ____ indicates dehydration

20 : 1

In what order are Arterial Blood gasses given in a panel?

Ex: 7.54 / 38 / 95 / 25 / 98

pH / pCO2 / pO2 / HCO3 / O2 saturation

Anion Gap formula

(Include normal range)

Na - Cl - HCO3

(Range: 3-12)

pH equation

Weak acid

pH = pKa + log (salt/acid)

pH equation

Weak base

pH = pKa + log (base/salt)

How to determine pKa when given pKb?

14 - pKb = pKa

% ionization

weak acid

100 / 1 + 10^(pKa - pH)

% ionization

weak base

100 / 1 + 10^(pH - pKa)

What percentage of calcium citrate is elemental calcium?

21%

What percentage of calcium carbonate is elemental calcium?

40%

Which calcium salt is acid-dependent and which is acid-independent?

- Calcium carbonate is acid-dependent (must be taken with food)

- Calcium citrate is acid-independent (w/o regard to food)

Which calcium slat is a phosphate binder and should not be used for calcium supplementation?

Calcium acetate (contains 25% elemental calcium, however the absorption is poor)

Absolute Neutrophil Count (ANC)

WBC x [%segs + % bands)/100]

ANC corresponding ranges:

- Normal:

- Neutropenia:

- Severe neutropenia:

- Profound neutropenia:

- Normal: 2200 - 8000

- Neutropenia: < 1000

- Severe neutropenia: < 500

- Profound neutropenia: < 100

Aminophylline to Theophylline Conversion

"ATM"

Aminophylline --> Theophylline --> Multiply by 0.8