Shares in Ranbaxy Laboratories have slipped after the Indian drugmaker recalled certain lots in the USA of atorvastatin, its generic version of Pfizer's cholesterol-lowerer blockbuster Lipitor.

The company issued a statement saying that the recall affects 10mg 20mg and 40mg dosage strengths, packaged in 90 and 500 count-bottles "and only with respect to certain select lot numbers". The recall does not affect the 80mg tablets.

Ranbaxy added that the recall is being conducted for batches that may contain a foreign substance, ie small glass particles approximately less than 1mm in size. The voluntary recall, which "is being conducted with the full knowledge of the US Food and Drug Administration" is being carried out due to "an abundance of caution, and in keeping the safety of our customers in mind".

Ranbaxy, which is majority-owned by Daiichi Sankyo, said the recall will disrupt supplies of atorvastatin in the US market while it conducts an investigation. The latter should take about two weeks.

Generic Lipitor contributed almost $600 million to Ranbaxy's coffers for the first six months of the year, as the firm enjoyed 180-day exclusivity to sell its copy after Pfizer's patent expired on November 30, 2011. News of the recall is a blow and echoes Ranbaxy's previous problems with the FDA over manufacturing violations discovered in 2009 at its Dewas and Paonta Sahib plants, a dispute that was only resolved this year.