Top Pfizer research executive Martin Mackay has left the world's biggest drugmaker to head research at rival AstraZeneca as both companies brace for patent expirations on their top-selling medications.

Pfizer will consolidate its research and development under Mikael Dolsten, who had worked with Mackay as co-head of research and development since October in a split of duties created from the company's $67 billion merger with Wyeth. Pfizer is betting on drugs from Wyeth, where Dolsten served as research head, to help it endure plunging sales of its Lipitor cholesterol fighter when the world's top-selling drug faces generic rivals late next year.

Pfizer said Mackay, a soft-spoken and personable native of Scotland, had resigned and left the company "immediately." He will take on the new role of president of R&D at London-based AstraZeneca on July 1. Mackay had been the company's global research chief for two years and, after the Wyeth merger, led PharmaTherapeutics research at Pfizer, involving conventional drugs made from chemicals. Dolsten oversaw research of BioTherapeutics, biotech drugs made from complex proteins grown in living cells.

"That structure was unusual," Leerink Swann analyst Seamus Fernandez said. "It struck me as potentially a vetting period for Dolsten," to better assess his leadership skills.

Morningstar analyst Damien Conover said Dolsten is not well known by Wall Street and will be under pressure to galvanize Pfizer's underperforming laboratories. Wyeth brought Pfizer currently marketed biotech drugs, such as blockbuster arthritis drug Enbrel, but did not greatly remedy Pfizer's dearth of drugs in late-stage testing.

"So Dolsten has a pipeline that is not as strong as it needs to be to offset Lipitor's patent loss," Conover said. He noted, however, that Pfizer is developing treatments for Alzheimer's disease, arthritis and blood clots that have blockbuster sales potential should they eventually be approved.

R&D Pedigree

Dolsten has a medical degree from the University of Lund in Sweden and led drug research for Germany's Boehringer Ingelheim before joining Wyeth. He also had senior roles with other drugmakers, including AstraZeneca and Pharmacia & Upjohn.

"Anyone in leadership in R&D at Boerhinger Ingelheim, which has been an incredibly productive R&D organization over the last several years, should probably be viewed reasonably positively," Fernandez said.

Pfizer itself has produced few big drugs since introducing anti-impotence pill Viagra in 1998, despite its later acquisitions of U.S. rivals Warner-Lambert and Pharmacia and an industry-topping annual $8 billion research budget.

"The Wyeth deal buys Pfizer a little more time after Lipitor's patent expires, but the company really needs to start kicking out some new drugs," said Miller Tabak analyst Les Funtleyder. "Otherwise, it will have to change direction, and move deeper into related areas of healthcare such as generics or consumer products."

For its part, AstraZeneca separated the two stages of R&D by having a head of drug discovery and a head of drug development, leaving some investors uncertain about its focus. Mackay's appointment brings the two roles together as the company overhauls R&D to prepare for patent expiries on top drugs like Nexium, for acid reflux, and Seroquel, for schizophrenia.

AstraZeneca spokesman Neil McCrae said a unified head of R&D would speed up decision-making and help allocate resources between different projects at a time of major change.

"We set out our strategy for R&D in January, which calls for some significant changes as we seek to improve the productivity of our pipeline," he said. "In addition, since the acquisition of MedImmune, it has become clear that we need a single point of accountability to manage the entire R&D portfolio."

Mackay has extensive experience working on both sides of the Atlantic. Prior to joining Pfizer in 1995, he focused on research into central nervous system diseases at Ciba-Geigy, now part of Novartis AG.