The breast cancer drug tamoxifen may offer a new treatment against a deadly drug-resistant "superbug," a new study suggests.

Researchers have spent decades trying to find an effective therapy for methicillin-resistant staphylococcus aureus (MRSA) but have had little success. MRSA is resistant to most antibiotics and is estimated to have contributed to 5,000 deaths in the United States in 2013, the Washington Post reported.

It's known that tamoxifen boosts the body's defense system against infection. So researchers at the University of California, San Diego gave tamoxifen to mice and then injected them with normally lethal levels of MRSA.

Tamoxifen improved the rodents' chances of survival by one-third, according to the study in the journal Nature Communications.

These are early findings and more research is needed before this approach can be tested in people, investigator Victor Nizet told the San Diego Union Tribune, but added that he hopes the study "inspires clinical trials in patients with severe infections," the Post reported.