This seems to have caught Wall Street by surprsie. George Barrett was liked by investors and his departure is causing some analysts to wonder aloud whether the changover will be an issue. Barrett will be replaced by Bill Marth, who is currently ceo and president of Teva USA.

Barrett, meanwhile, is joining Cardinal Health, one of the big US drug wholsalers, as vice chairman and will also serve as ceo of Cardinal’s health-care supply chain services sector, according to a statement. Barrett, 53, will remain with Teva through January to assist in the transition and Marth, 53, will assume the additional role of CEO of Teva North America immediately, Teva said in its own statement.

Teva stock fell more than 4 percent earlier on the news, while Cardinal shares were up.

Marth has run the U.S. generics business where he has handled much of the commercial activities since 2002 and has been president and CEO of Teva USA since 2005. And he’s overseen a number of significant product launches, notably the December launch of generic Protonix, and two of the largest launches in the history of US generics - Simvastatin and Pravastatin in 2006, Reuters reminds us.

In a research note, Wachovia analyst Michael Tong wrote that disruption caused by Barrett’s departure should be minimal, citing Teva’s “deep bench of management talent.” But he added there is “little margin for error … Although we have confidence in TEVA’s management, we cannot ignore the loss of experience…There is little margin for error in management transition and continued execution of the core business.

CIBC World Markets analyst Elliot Wilbur tells Reuters, “Barrett is a popular guy on Wall Street, though we see little, if any, short-term impact on the stock from his departure. Teva has charged forward unscathed through significant top-level management change over the past several years, and we expect this situation to be no different.”

Deutsche Bank analyst Ross Muken said he views the move as a positive for Cardinal as it fills a void that has been filled by Cardinal’s chief financial officer. “We expect Barrett to look to re-energize growth and margin expansion in the business, which has seen some recent struggles but remains a solid platform.”

Corey Davis, an analyst with Natixis Bleichroeder, views Barrett’s move as a surprise. “It’s unclear why he left, but we’d surmise is that he has aspirations of becoming the top dog at Cardinal. He had every opportunity to become the CEO of Teva last year, but for personal reasons, was unwilling to move to Israel,” Davis wrote in a research note.