The player can switch patients at any time during the operation.

As part of these deals, drug companies pay pharmacy chains for drug promotions that can range from simple refill reminders to efforts to switch patients to higher-priced drugs.

But James Tallon, a lawyer for Merck-Medco, described how his client made money in the past by persuading doctors to switch patients to particular drugs.

Merck said it planned to persuade doctors to switch patients to Vytorin before 2006, when generic competition starts in the United States for Zocor, the company's biggest drug.

Schering-Plough is also working to persuade doctors to switch patients to Clarinex, a similar prescription drug the company hopes will absorb some of Claritin's multibillion-dollar annual sales.

Now AstraZeneca is trying to persuade doctors to switch patients from Prilosec to a similar successor drug, Nexium.

When Potter offers to switch patients with him, he declines and goes to work, indicating that his recovery is complete.

The system could also lead doctors to switch patients to drugs preferred by benefit managers.

The company has been trying to switch patients to its newer drug, Flovent, which it says is more effective.

But she said she would be inclined to switch other patients off Lipitor onto generic Zocor, also called simvastatin, if the price difference was significant.