McKesson Corp., the nation's largest drug wholesaler, agreed to buy closely held Baker/Automated Prescription Systems Inc. for about $154.9 million in stock and debt to expand its line of automated drug-dispensing systems. San Francisco-based McKesson would pay about 1.3 million shares and assume about $48 million in debt and other liabilities for Pineville, La.-based Baker/APS, the top maker of automated counting and dispensing systems for U.S. retail, mail-order and outpatient pharmacies. Baker/APS had revenue of $31 million last year. Its systems count and package drugs for large distributors such as Longs Drug Stores Corp. McKesson would keep all 190 Baker/APS employees, and operations would remain in Louisiana. McKesson shares fell $1.25 to close at $81 on the New York Stock Exchange.