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For Overweight Patients, Dosing Chemotherapy Based on Total Body Weight Does Not Lead to More Toxicities

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ANAHEIM—Overweight as well as obese chemo therapy recipients who are dosed according to total body weight do not experience more adverse drug events or cycle delays than normal weight recipients.

The finding, which comes from a 10-year retrospective analysis of patients with gastrointestinal (GI) cancers, should allay concerns about overdosing and the potential for increased toxicities when calculating the chemotherapy dose using total body weight, said lead investigator Tiffany Dea, PharmD.

Dea and colleagues sought to determine how chemotherapy is dosed in practice in normal weight, overweight, and obese patients as well as that dose’s impact on adverse drug events. They assessed 42 patients with GI cancers identified through a tumor registry who were treated at the San Francisco Veterans Affairs Medi cal Center.

The chemotherapy drugs used in treatment were bevacizumab, capecitabine, cetuximab, cisplatin, epirubicin, fluorouracil, irinotecan, leucovorin, mitomycin, and oxaliplatin.

Of the 42 patients included, 13 were normal weight (body mass index [BMI], 18.5-24.9 kg/m2), 22 were overweight (BMI, 25-29.9 kg/m2), and seven were obese (BMI, >30 kg/m2).

“Most of our oncology fellows are dosing on total body weight for overweight patients,” said Dea, an oncology pharmacist. “There is some literature out there that says that you shouldn’t cap the body surface area, but there’s no rationale for that. A lot of oncologists still prefer to dose based on adjusted or capped body surface area.”

All 13 of the normal weight patients were dosed using total body weight. Of the 29 overweight or obese patients, 21 were dosed using total body weight— one using adjusted body weight, five using capped body surface area, and two using both total body weight and capped body surface area.

“We didn’t find that overweight or obese patients had more side effects than normal weight patients,” said Dea. Grade 1 or 2 toxicities were experienced by 100% of the normal weight patients and 79.3% (16) of the overweight/ obese patients. Of the overweight or obese patients experiencing toxicities, 76% were dosed according to total body weight compared with 100% dosed using adjusted body weight and 60% dosed using capped body surface area.

“In looking at the cancer stage, more normal weight patients were in stage IV disease; in the overweight/obese category, there were more in stage III disease,” she said. “Whether or not that may have been a factor in the rate of side effects isn’t known.”

Some 54% of normal weight patients had stage IV disease, 50% of overweight patients had stage III disease, and 43% of obese patients had stage II disease.

Thirty-one percent of normal weight patients had decreases in their dosage between cycle 1 and 2 compared with 14% of overweight/obese patients. Second cycle delays were also more frequent in the normal weight patients versus the overweight/obese patients (31% vs 28%, respectively).

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