On Nov. 30, 2011, the patent for Lipitor, the cholesterol-lowering drug that defined the term “blockbuster,” expired. Over its lifetime, it is estimated that Lipitor generated over $100 billion in sales for its parent company, Pfizer, since its introduction in 1997.

Companies have been waiting in the wings to pick up the rights to the generic version. Watson Labs launched an authorized generic version of Lipitor on Nov. 30. Under the terms of an exclusive supply and distribution agreement, Pfizer will manufacture and supply Watson with all dosage strengths of the authorized generic product, and Watson will market and distribute the product in the US. In turn, Pfizer will receive a share of the net sales.

Ranbaxy Labs picked up last-minute approval from FDA to market generic atorvastatin in the US under the coveted first-to-file spot, that gives them a 180-day period of marketing co-exclusivity that they will share with Watson. The drug will be manufactured by Ohm Laboratories in New Brunswick, NJ, according to the FDA release.  According to Ranbaxy’s press release , a portion of the profits from sales of atorvastatin during Ranbaxy’s 180-day first-to-file exclusivity period will be paid to Teva, but further details of that agreement have not been disclosed.

Pfizer does not seem willing to jump quietly off the patent cliff. In an effort to maintain market share and promote brand loyalty, it has stepped up marketing in recent months, and is offering rebate coupons to insured patients to bring copays for the branded version in line with those for generic versions. It has also entered into controversial agreements with some pharmacy benefit managers in which they will receive rebates if they block generic prescriptions, a move that has sparked concern among members of Congress.

Because this particular drug has such a huge market, there’s a lot of money at stake. Generics are low margin, but low margins on a high-volume product can still make handsome profits. In developing countries, branded generics are popular, because they give patients the comfort of brand-name recognition, and an expectation of quality greater than that from nonbranded generics. That model has never caught on in the US, but Pfizer’s attempts to hold on to such a lucrative product makes me wonder whether its time will come.