Pfizer's Lipitor, which is the world's best-selling drug, lost patent protection Nov. 30.
Along with Pfizer, the other companies to receive letters include Medco Health Solutions, Express Scripts, Catalyst Rx, Coventry Health Care and UnitedHealth Group.
“We are concerned that arrangements like this will hinder access to generic drugs today and in the future,” the senators said in the letter to Pfizer. “Without the prospect of true competition, generic drug manufacturers will be hesitant to invest the time and resources required to bring low-cost generic drugs to the market.”
Baucus, Grassley and Kohl requested the companies provide a list of agreements that block generics or favor brand-name drugs, as well as documents related to the Lipitor agreement.
Pharmacists United for Truth and Transparency, a coalition of independent pharmacists and pharmacy owners, released documents in November that showed 1.2 million fully insured Coventry Health Care members will pay a reduced generic co-payment for atorvastatin, the generic version of Lipitor, but will continue to receive the brand-name drug. The documents also showed that PBMs had notified pharmacies that they would not cover atorvastatin when it became available.
At that time, Pfizer said in a statement that the agreement, which provides Lipitor at or below generic costs, would not increase costs for most payers that participate in its program.
Express Scripts said it recommends against blocking the generic version of Lipitor at the retail level, but the company does allow it, an Express Scripts spokesman said in a statement.
"It is up to the plan sponsor to mandate coverage of a brand as a generic and a generic as a brand in the retail setting," the statement said. "It is not a decision made by a PBM."