Canterbury DHB

Context

Calculating the Dose of Cytotoxic Drugs

Creatinine Clearance

There are various ways of assessing renal function before chemotherapy. The most appropriate method will depend on the drug and schedule to be used. In general, we recommend the Cockcroft and Gault formula.

Normal range for the estimated GFR and creatinine clearance is >90 mL/min.

Estimated GFR reported by Canterbury Health Laboratories gives an indication of renal function, but should not be used to determine drug dosing. It is only reliable under steady state conditions (stable creatinine for more than four days) and does not account for body size. This leads to over and underestimates of renal function at the extremes of body size.

Note: A 24 hour urine collection for creatinine clearance is not routinely recommended. A nuclear medicine scan is also rarely done. It may be indicated when chemotherapy drugs with a high risk of renal toxicity (e.g. Cisplatin) are used.

Weight and Body Surface Area (BSA)

Chemotherapy drug dosage is usually calculated using BSA or per kg body weight. Some schedules simply require a set dose/day regardless of size.

The relationship between body weight and the dose of the chemotherapy drug that should be administered is controversial. We recommend measuring the actual body weight, recording the ideal body weight, and the patient’s height. Calculate the patient’s BSA using their actual body weight.

If the patient’s actual body weight is >30% above the ideal body weight, some dose reduction is usually recommended. Take the mid-point between these two weights and use this adjusted body weight for per kg dosage or for BSA calculations.

Example: actual body weight 125 kg, ideal body weight 85 kg, adjusted body weight = 105 kg.

Note: This adjustment method is not entirely satisfactory but it is simple to use, and is recommended until some better method of dose adjustment is found.

Note:

Determine Ideal Body Weight

See the Ideal Body Weight table or use the Ideal Weight Calculator.

Calculate Surface Area

Use the Online BSA Calculators:

About this Canterbury DHB document (11668):

Document Owner:

Steve Gibbons and Fiona Stone (see Who's Who)

Issue Date:

March 2017

Next Review:

March 2020

Keywords:

Note: Only the electronic version is controlled. Once printed, this is no longer a controlled document. Disclaimer

Topic Code: 11668