An observational study of a large United Kingdom primary care database showed that switching patients from Pfizer's Lipitor (atorvastatin calcium) tablets to simvastatin was associated with a 30 per cent increase in the relative risk of major cardiovascular events, including heart attacks, strokes and certain types of heart surgeries, or death compared to patients who remained on Lipitor therapy.

This analysis was presented at the European Society of Cardiology Congress 2007 and is also in press at The British Journal of Cardiology.

The data, which included records from October 1997 to June 2005, were generated from a retrospective analysis of a medical database of anonymous patient records entered by general practitioners in the United Kingdom known as The Health Improvement Network (THIN). The analysis included 11,520 patients (2,511 patients who had taken Lipitor for six months or more and were switched to simvastatin vs. 9,009 patients who were taking Lipitor for six months or more and then remained on Lipitor therapy). Reasons for switching were not available from the database. Since patients were not randomly assigned to each group, the two treatment groups were matched based on certain risk factors and statistical adjustments were made to address any residual imbalances. As with all observational studies, the findings should be regarded as hypothesis generating.

"Today, many health care payors including governments and managed care companies are encouraging patients who are well-established on one therapy to switch to a different statin therapy," said Dr Michael Berelowitz, senior vice president of Pfizer's global medical division. "This study raises concerns about those policies. It suggests the potential for poorer cardiovascular outcomes associated with switching patients from established Lipitor therapy to simvastatin."

A secondary analysis of the same data showed that patients who were switched from Lipitor to simvastatin were more than twice as likely to discontinue their treatment compared to those who remained on Lipitor therapy. The reasons for discontinuation were not available from the database, though disruption in treatment has been associated with poor adherence in previous studies of statins and other medications.

"The results of this analysis complement the large body of evidence from multiple clinical trials demonstrating the cardiovascular benefits of Lipitor," said Dr Berelowitz. "Observational studies help the medical community better appreciate what is really happening in doctors' offices, and are commonly used by healthcare payors to set medical practice guidelines. This analysis highlights the need to carefully consider individual patient circumstances and cardiovascular risk because indiscriminate switching may adversely affect some patients".

The primary endpoint was time to a first major cardiovascular event, defined as heart attack, stroke, or coronary revascularization (a type of heart surgery), or all-cause death. There was a statistically significant 30 per cent increase in the relative risk of the primary endpoint.