Akorn Inc. plans to pay $640 million in cash to buy fellow generic drugmaker Hi-Tech Pharmacal Co. Inc. in a deal that it expects will help boost its adjusted earnings immediately.

Lake Forest, Illinois-based Akorn said that it will pay $43.50 for each share of Amityville, New York-based Hi-Tech. That represents a premium of more than 23 percent over Hi-Tech's closing price Monday of $35.21.