August 29, 2012

Obese, Overweight Patients Endangered
by Inadequate Chemotherapy Doses

Alexandria, VA—Pharmacists and other health care providers should use body weight to determine appropriate chemotherapy dosage, according to a new guideline released by the American Society of Clinical Oncology (ASCO), which is seeking to provide optimal care for the growing number of patients who are overweight or obese.

The guideline released this summer, " Appropriate Chemotherapy Dosing for Obese Adult Patients With Cancer,” covers both intravenous and oral chemotherapy. Most (60%) U.S. adults fall into the overweight or obese body mass index category, yet when it comes to chemotherapy, overweight and obese patients currently receive limited or reduced doses, according to the guideline. To remedy that, the guideline strongly recommends using actual body weight to determine the appropriate cytotoxic chemotherapy dosing essential for cure.

“This guideline will reduce the uncertainty and variation of chemotherapy dosing in clinical practice and result in more consistent evidence-based treatment and improved clinical outcomes,” said Gary H. Lyman, MD, MPH, FASCO, FRCP, of Duke University School of Medicine and co-chair of the expert panel that developed the recommendations.

The new guideline emphasizes that most concerns about toxicity or overdosing in obese patients with cancer are unfounded if actual body weight is used for determining dosage. It notes that the safety of full weight-based dosing has been confirmed in clinical studies, pointing out, for example, that obese patients are less likely to have myelosuppression when doses of chemotherapy agents are calculated according to their body weight.

In general, the panel found that fixed-dose chemotherapy is rarely appropriate, but recommends it for a few selected agents. The authors also recommend further research on chemotherapy treatment for obese patients.

“Many oncologists are not aware that full weight-based doses are used in patients on clinical trials,” said expert panel member Jennifer J. Griggs, MD, MPH, of the University of Michigan. “Disseminating the evidence against dose limits is one way to overcome the under-dosing we have seen in up to 40% of patients. This is particularly important given the prevalence of obesity and the relationship between obesity and cancer incidence and outcome.”

If toxicity forces the reduction of a weight-based dose, the guideline suggests returning to the full dose with careful monitoring when the toxicity is resolved.

The guideline cautions that comorbidities should be considered when determining dosage, whatever the patient’s weight.

U.S. Pharmacist Social Connect