Regulators in the USA have issued Pfizer with a warning over what they claim is the company’s failure to report serious and unexpected potential side effects from some of its drugs in a timely fashion.

In a 12-page letter addressed to Pfizer chief executive Jeffrey Kindler, the US Food and Drug Admininstration says delays in reporting side effects date back from 2004 and have increased since then. The treatments cited in the letter include the cholesterol-lowering blockbuster Lipitor (atorvastatin) and the erectile dysfunction drug Viagra (sildenafil).

Ronald Pace, chief of the agency's New York office, writes that the FDA “expects drug manufacturers to establish and implement reasonable mechanisms to assure that all serious and unexpected experiences are promptly recorded and investigated”. For example, while Viagra was known to cause serious visual problems, Pfizer failed to report cases within the agency's 15-day deadline “by misclassifying and/or downgrading reports to non-serious without reasonable justification."

Regarding the now-withdrawn painkiller Bextra, (valdecoxib), the FDA granted Pfizer a waiver allowing 60 days to forward any complaints but that deadline was missed. According to the agency, the New York-based major initially blamed the problems on a new computerised system and told the FDA in September 2009 that it would update user manuals, better train its staff and take other actions.

However the FDA warning letter states that Pfizer’s actions were “inadequate”, and although the company claimed that its reporting improved after May 2009, it did not include any data backing up that claim. Also the agency says that 4% of Pfizer's 80,560 reports were sent late from March 2006 through December 2008, climbing to 9% from December 2008 to June 2009.

Dr Pace has asked Mr Kindler to arrange a meeting between the company and the agency over the violations. He added that failure to sort out the problems could result in legal action without notice and the FDA could delay action in approving Pfizer’s drugs, among other penalties.

Pfizer says it will work with the FDA to “assure optimal surveillance and reporting of post-marketing adverse events”. However it added that individual reports are just one part of its overall monitoring and believes “we provide complete and accurate data to determine the benefit and risk profile for all of our medicines, and to enable their safe and appropriate use”.