Amazon.com Inc said on Thursday that it would buy online pharmacy PillPack for an undisclosed amount, sending shares of drug distributors and drug retailers down. Drug retailers CVS Health and Walgreens Boots Alliance plunged 7 percent each in premarket trading. Shares of drug wholesalers Mckesson Corp, Cardinal Health and AmerisourceBergen were also down. Amazon, Berkshire Hathaway and JPMorgan announced a joint venture in January, saying U.S. healthcare costs were rising too fast and holding back economic growth. The three companies said they would use big-data analysis and other high-tech tools to improve care and cut waste. Walmart Inc was looking to buy PillPack for under $1 billion, CNBC had reported in April. Privately-held PillPack caters to patients who take multiple daily prescriptions and delivers medications in pre-sorted dose packaging and coordinates refills and renewals. The deal is expected to close during the second half of 2018.