Switching from atorvastatin to simvastatin in patients at high cardiovascular risk: effects on low-density lipoprotein cholesterol.

Since generic simvastatin became available in the United States in 2006, approximately one million patients have switched from atorvastatin to simvastatin. We examined the association between switching from atorvastatin to simvastatin and changes in low-density lipoprotein cholesterol (LDL-C) levels in clinical practice. We compared atorvastatin-treated patients at high cardiovascular risk who switched to simvastatin between June 2006 and July 2007 with randomly selected matched patients who remained on atorvastatin and evaluated changes in LDL-C and percentage of patients reaching LDL-C less than 100 mg/dL. Of patients who switched from atorvastatin to simvastatin, the majority were excluded as a result of lack of LDL-C measurements, leaving 383 patients in the analysis. Among these, 122 (31.9%) switched to a simvastatin dose that was less than therapeutically equivalent to their prior atorvastatin dose. Compared with control subjects, switched patients were less likely to reach an LDL-C less than 100 mg/dL (68.4% versus 74.0%; odds ratio, 0.76; 95% confidence interval, 0.59-0.99; P = 0.041) and had higher measured LDL-C (91.4 versus 87.2 mg/dL; P = 0.009). Switched patients who were not prescribed a higher milligram dose of simvastatin were significantly less likely to reach an LDL-C less than 100 mg/dL (62.3% versus 74.0%; odds ratio, 0.55; 95% confidence interval, 0.36-0.84; P = 0.006) and had higher LDL-C (95.1 versus 87.2 mg/dL; P = 0.002) than control subjects. A large proportion of patients who switch from atorvastatin to simvastatin are prescribed doses that are not therapeutically equivalent, and these patients were significantly less likely to meet LDL-C treatment goals compared with patients who remained on atorvastatin.