Pfizer HQ

Pfizer has vowed to "vigorously" defend itself against claims that it conspired with India’s Ranbaxy Laboratories to delay sales of generic versions of Lipitor, the world’s best selling drug.

Five US filed a lawsuit against the companies on 5 July 2012 in New Jersey, accusing the companies of an "overarching anticompetitive scheme" to keep generic versions of the cholesterol drug off the market until November 30 2011, 20 months after the original patent expired, reports Reuters.

Walgreen Co, Kroger Co, Safeway Inc, SuperValu and HEB Grocery Co said the defendants obtained a fraudulent patent, entered a price-fixing agreement to delay cheater generics and entered arrangements with pharmacy benefit managers to force retailers to buy more Lipitor (atorvastatin calcium).

Pfizer denies the plaintiffs’ claims and will defend itself vigorously, spokesman Christopher Loder told the news agency.

"We are confident that Pfizer’s procurement and enforcement of its Lipitor patents was at all times proper and lawful," he added.

Lipitor sales in 2011 totalled $9.6bn, but in the first quarter of 2012, the drug’s sales fell about 42% to $1.4bn from $2.39bn a year earlier, a drop that Pfizer attributed to the loss of US exclusivity.

Image: Pfizer’s world headquarters in Manhattan, New York.