Genentech has aggressively promoted Lucentis to doctors to encourage them to switch, even paying rebates to those who use large amounts of Lucentis, a practice that critics have described as improper but the company says is legal. For Genentech, the stakes are high. Lucentis is one of its top products, generating $1.3 billion in sales in the first nine months of this year, an increase of 5 percent over that period last year.

Even with widespread Avastin use, injecting Lucentis remains one of Medicare’s costliest procedures. In 2010, Medicare paid $1 billion to treat macular degeneration patients with Lucentis, while it spent $27 million for such patients treated with Avastin, according to a 2012 study from the Office of the Inspector General for the Department of Health and Human Services.

In 2011, the office determined that if all patients being treated with Lucentis were instead given Avastin, the federal government would have saved about $1.4 billion.

A review released this year of nine clinical trials showed that Avastin and Lucentis had similar safety profiles and that Avastin did not appear to increase deaths or serious side effects. The review was conducted by the nonprofit Cochrane Collaboration.

Still, several doctors, including those who speak on behalf of Lucentis and those who do not, said the choice between Avastin and Lucentis was not simply a matter of cost.

For example, Lucentis is specially prepared to be injected into the eye, but Avastin must be divided into smaller doses by outside compounding pharmacies, which can lead to contamination in rare cases. In 2011, more than a dozen people developed severe eye infections, and some were blinded, after they received injections of contaminated Avastin.

Some doctors say there is no good reason to use Lucentis more frequently than Avastin.

“They keep talking about evidence-based medicine, and they keep pretending the corporate-sponsored research is nonbiased,” said J. Gregory Rosenthal, a retina specialist in Toledo who has become an outspoken critic of Lucentis and Eylea. “The evidence says that Avastin has at least the clinical efficacy of Lucentis and is perhaps safer.”