The CMS allows doctors to prescribe Medicare patients two different drugs for age-related macular degeneration, one of which costs an average of $54 a dose and the other costs $2,030. Yet 43% of CMS' prescriptions in 2008 and 2009 were for the more-expensive drug—a preference that cost an extra $1.1 billion, according to federal auditors.

However, only one of the drugs, Lucentis, is approved by the Food and Drug Administration for treatment of wet age-related macular degeneration, the leading cause of vision loss in senior citizens. The other, Avastin, is widely used off label.

The maker of the two drugs, Genentech, said physicians should consider other factors than just price when choosing between Lucentis and Avastin, especially when the cheaper therapy has been found to carry greater risks of stroke, death and eye infections.

Lucentis was approved for use on macular degeneration by the FDA in 2006, and it costs roughly 38 times more than Avastin, a colorectal cancer drug that is commonly prescribed to prevent vision loss, even though the FDA never approved it for that use. Despite strict prohibitions on promoting off-label uses of drugs by the FDA, the CMS does reimburse for off-label prescriptions, including Avastin for wet age-related macular degeneration.

An audit by the HHS office of inspector general calculated that in 2008 and 2009, Lucentis comprised 43% of all individual treatments for the condition, but 97% of CMS' total pharmaceutical costs.

Lucentis was developed in the laboratory specifically for macular degeneration, using a modified fragment of the antibody Avastin. The National Eye Institute in April reported that early results in a clinical trial had found the drugs performed the same in preventing changes in visual acuity when administered on the same dosing schedule.

Genentech, the San Francisco-based subsidiary of Swiss pharmaceutical firm Roche Holding, said Lucentis is the best drug for wet age-related macular degeneration because it was specifically designed to treat it. Company spokesman Terence Hurley said in an e-mail that “a growing body of evidence” suggests injecting Avastin into the eye can create more complications and carries an increased risk of stroke and death.

“The price of Lucentis allows us to continue discovering medicines for people with serious eye diseases,” Hurley's statement said. “We are committed to ensuring that the people who need our medicines do not go without treatment due to financial barriers.”