Pfizer is hoping to sell an over-the-counter version of its cholesterol-lowering drug Lipitor (atorvastatin).

The company loses its patent on the world’s best-selling drug in November and so hopes to squeeze sales from its blockbuster medicine in the months after the expiration date.

Pfizer, however, could struggle to sell a non-prescription version of the drug because the US Food and Drug Administration has previously rejected the sale of over-the-counter versions of cholesterol drugs in the same class as Lipitor, known as statins, reports the Wall Street Journal.

The US patent protection of Lipitor was initially scheduled to expire in June 2011, but Pfizer made an agreement with Indian pharmaceutical company Ranbaxy Laboratories to delay the generic launch in the US until November.

Lipitor currently generates $11bn in sales a year for Pfizer.