PHP 528: EXAM 2: Chemotherapy Calculations

Ways to Dose Chemotherapy

-Body Surface Area (most common, standardizes dose across spectrum)

-Weight-based (more common in peds)

-Flat dose (more common with PO therapies)

Body Surface Area: Limitations

-Estimation

-No correlation with renal or hepatic function

-Not developed for use in obese patients

Body Surface Area: Helpful tips

-Pounds to Kilograms: 2.2 lbs = 1 kg

-Inches to Centimeters: 1 in = 2.54 cm

-Round weight to 1 decimal place

=> 95.23 kg -> 95.2 kg

-Round BSA to 2 decimal places

=> 1.263 m2 -> 1.26 m2

Dosing in Obese Patients

-Actual body weight (ex. BSA = 2.34 m2)

-Ideal body weight (IBW) (ex. BSA = 1.71 m2)

=> IBW Men = 50 kg + 2.3 kg x (height, in - 60)

=> IBW Women = 45.5 kg + 2.3 kg x (height, in - 60)

-Adjusted body weight

=> AdjBW = IBW + 0.4 x (actual body weight - IBW)

-BSA capping not typically recommended

=> Unless dose exceeds maximum recommended dose of the drug

Dosing in Obese Patients: ASCO 2021

-Recommended to use actual body weight

-Dose capping based on BSA not typically recommended

=> Unless dose exceeds maximum recommended dose of the drug

Calculating Renal Function

-Cockcroft-Gault (>18 yo)

-Modified (Bedside) Schwartz (<18 yo)

*our pt is 23

Chemotherapy Dosing in Dialysis

-Consider size of the molecule

=> Is it likely to be cleared by dialysis?

-Is the drug eliminated renally? (then need to look at dose adjustments)

-Are there any specific recommendations in treatment protocol?

*will be given dose adjustments)

Hepatic Dose Adjustments: Considerations

-Is the drug hepatically cleared?

-Is the drug hepatotoxic?

Hepatic Dose Adjustments: Parameters for dose adjustments vary by drug and protocol

-AST/ALT

-Total bilirubin

-Child-Pugh score

-Alkaline phosphatase

*will be given dose adjustments, but we need to figure out if pt needs to be adjusted

Underweight Patients

-Limited literature available

-Current literature supports use of actual body weight

Amputation

Rule of 9's

(4.5% in each arm)

Amputation: Body Part Percentage

Amputation Steps

1. Calculate BSA based on patient's pre-amputation height and weight

2. Subtract surface area of the amputated parts (from pre-amputation weight)

=> Rule of nines

OR

=> Body Part Percentage

Absolute Neutrophil Count Formula

Absolute Neutrophil Count Interpretation

-ANC 1001-1499 = mild neutropenia

-ANC 500-999 = moderate neutropenia

-ANC <500 = severe neutropenia

Question 9: What other helpful equations do I need to know?

Carboplatin dosing

-Calvert formula: Total dose (mg) = Target AUC × (GFR + 25)

-Target AUC depends on indication

Equations to Know