Almost $3 billion a year in expensive cancer drugs are wasted because their single-use packages contain more medication than is needed -- and the leftover drug is thrown away for safety reasons, according to a new analysis by researchers.

The study focused on 20 cancer drugs that are infused -- administered intravenously or injected -- by doctors' offices or hospitals. These come in dosages based on patients' weights and body sizes, but often the doses are too large and the remainder is tossed out, the analysis found.

"It’s literally paying for drugs that go in the trash," said Peter Bach, director of the Center for Health Policy and Outcomes at Memorial Sloan Kettering Cancer Center in New York. Bach co-authored the study, which was published Tuesday in BMJ, formerly known as British Medical Journal. To increase profits, pharmaceutical companies "are finding a way to charge patients and insurers for drugs that they don't even take," he said.

The study concluded that Medicare and private insurers, as well as patients, pay companies about $1.8 billion a year for medications that are thrown away. They pay another $1 billion to doctors and hospitals as price markups on those discarded medications, according to the study. The analysis was conducted against the backdrop of rapidly rising price increases in both new and older cancer drugs.

“This study reveals that billions of dollars are wasted on expensive cancer drugs, due to the way they are packaged in single doses.  This practice greatly inflates profits but is waste that we can no longer afford," John Rother, president and chief executive of the National Coalition on Health Care, said in an email.

But Allyson Funk, senior director of communications at the trade group Pharmaceutical Research and Manufacturers of America noted in a statement that developing and manufacturing cancer medications remains extremely complex and subject to strict regulation by the Food and Drug Administration.

“Decisions regarding vial size are tied to a product’s initially approved dosage and labeled use, taking into account that different patients will have different needs," she said. "Vial fill size must be approved by FDA as part of the sponsor’s drug application and any excess volume must meet FDA standards outlined in regulations." Any change in vial sizes requires FDA approval, which can take months, she said.

The FDA, which regulates the safety and effectiveness of drugs, doesn't have authority to weigh cost in considering medications, and Bach said he didn't think the agency could order drug companies to use certain vial sizes. But he said he thinks it could, and should, encourage the companies to sell their products in various vial sizes to minimize leftover medication.

An FDA statement noted that officials had not yet reviewed the article but that the agency "works with firms to make sure the proposed vial size is appropriate for the intended use of the product, especially where there are safety concerns about medication errors or the potential that excess drug could be used inappropriately to treat multiple patients from the same vial (which raises concerns about cross-contamination)."

The researchers who did the analysis also said government agencies should develop a consistent policy on whether a vial can be used on more than one patient. Though the Centers on Medicare and Medicaid Services encourages such "vial sharing," they said, the Centers for Disease Control and Prevention considers it unsafe.

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