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 UK 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. Pfizer said that as with all observational studies, the findings should be regarded as hypothesis generating.
Lipitor is the world's largest-selling drug and is still under patent in the US. However, Merck & Co.'s rival lipid-lowering therapy Zocor (simvastatin) lost its patent protection in 2006 and is now manufactured by several generics companies.
“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.”