Amazon unveiled plans to get into the pharmacy business Thursday with the acquisition of the online service PillPack.

Terms were not disclosed on the deal for PillPack, an online pharmacy which operates in all 50 U.S. states and offers pre-sorted dose packaging and home delivery.

Amazon has long been rumored to be interested in the pharmacy business, and its entry could disrupt a business dominated by large American chains such as CVS and Walgreens.

"PillPack's visionary team has a combination of deep pharmacy experience and a focus on technology," said Jeff Wilke, head of Amazon Worldwide Consumer.

"PillPack is meaningfully improving its customers' lives, and we want to help them continue making it easy for people to save time, simplify their lives, and feel healthier. We're excited to see what we can do together on behalf of customers over time."

CVS shares tumbled 8.6 percent in pre-market trade on the news, while Walgreens slumped 8.5 percent.

Amazon and PillPack said they expected to close the deal by the end of the year, subject to regulatory approval. Financial terms weren't disclosed.

TJ Parker, co-founder and CEO of PillPack, said the company which specializes in handling dose packaging and coordinates refills and renewals will benefit from a tie-up with Amazon.

"Together with Amazon, we are eager to continue working with partners across the healthcare industry to help people throughout the US who can benefit from a better pharmacy experience," Parker said in a statement.

The company, which has its primary pharmacy in Manchester, New Hampshire, ships to all states except Hawaii.