McDonald's Corp said on Tuesday it plans to reduce the use of antibiotics in its global beef supply, fueling projections that other restaurants will follow suit.

The move by the world's biggest fast-food chain addresses concerns that the overuse of antibiotics vital to fighting human infections in farm animals may diminish the drugs' effectiveness in people.

McDonald's becomes the biggest beef buyer to tackle the issue in cattle, potentially creating a new standard for livestock producers and threatening sales by drug companies such as Merck & Co and Elanco Animal Health.

"McDonald's iconic position and the fact that they're the largest single global purchaser of beef, make it hugely important," said David Wallinga, a senior health adviser for the environmental group Natural Resources Defense Council.

McDonald's said it will measure the use of antibiotics in its 10 biggest markets, including the United States, and set targets to curb their use by the end of 2020. The markets cover 85 percent of the company's global beef supply chain.

Under the McDonald's policy, medically important antibiotics cannot be used to routinely prevent disease in food animals in the supply chain.

The company does not expect the policy to raise hamburger prices, although franchisees set their own menu prices, spokeswoman Lauren Altmin said.

Franchisees operate about 90 percent of McDonald's restaurants.

The Animal Health Institute, which represents pharmaceutical companies, said it supported "judicious" use of antibiotics and that drug makers are developing alternatives.

Merck did not respond to a request for comment. Elanco said a small portion of its portfolio includes medically important feed-grade antibiotics. The drugs are used to treat conditions such as liver abscesses and respiratory diseases, for which there are not effective alternatives, spokeswoman Colleen Parr Dekker said

"It is important to ensure that policies do not move faster than science," she said.

Lack of alternatives to antibiotics to treat sick animals

Bob Smith, an Oklahoma-based cattle veterinarian for Veterinary Research and Consulting Services, said farmers have worked to cut back on antibiotic use while keeping cattle healthy. The lack of alternatives limits their options, however, when animals fall ill, he said.

"We will need those medically important antibiotics in meat production for a long, long time," Smith said. "We want to use those wisely."

The US Food and Drug Administration last year said sales and distribution of medically important antibiotics for food production fell 14 percent from 2015 to 2016, the first decline in year-to-year sales since the agency began collecting the data in 2009. Chicken accounted for 6 percent of the sales, while

swine and cattle came in at 37 percent and 43 percent, respectively.

Many restaurants and meat companies have moved away from using antibiotics in chicken production in recent years, in part because McDonald's did so. The Chicago-based chain has an outsize influence on farm practices due to its size.

Removing antibiotics from cattle is more difficult, experts said, because the animals live longer than chickens and have more chances to fall ill.

Hamburger chain Wendy's Co a year ago said it would buy about 15 percent of its beef beginning in 2018 from producers that have pledged to reduce by 20 percent their use of an antibiotic.

"What McDonald's is doing will hopefully start to shift the industry all together from over-using antibiotics," said Matt Wellington, antibiotics programme director for advocacy group US PIRG.