All five were asked about Amazon during earnings calls or analyst meetings in the past two months. Here are some of the highlights:
CEO John Hammergren was asked at the company's investor day in June if he views Amazon as a competitor or potential customer.
"The Amazon question is one we get frequently, and it's a question you could ask about any of our businesses," he said. "We clearly understand that Amazon has great capabilities to ship product in low unit of measures."
Hammergren said McKesson customers are "supported by significant sales and distribution resources" as well as controlled substance management. Getting beyond simple things like toothpaste sales is tough in pharmaceutical distribution, and "we're very well-positioned to continue to manage," he said.
During the company's earnings call last month, CEO Timothy Wentworth was asked if Express Scripts would be willing to reimburse Amazon for home delivery drugs.
"If Amazon were looking to become an efficient provider in networks, we would welcome that opportunity," he said. "We think Amazon is a great client for us. We think they are a company that if they choose to move in a direction, we'd be interested in working with them."
Analysts at Cardinal's analyst meeting in June wanted to know if Amazon could disrupt the supply chain.
"Amazon is an incredible company," CEO George Barrett said. "We have a lot of admiration for them. What we do, which is noteworthy, is operate in an intensely regulated business where the stakes are extremely high, where a failure to comply means a huge miss."
Barrett said Amazon has been a presence for a long time, "so we've built our strategies with an awareness that they're there." He added that it's interesting to think about Amazon as a potential partner, "but there are complexities there."