Therapeutic dose assessment of patient switching from atorvastatin to simvastatin.
OBJECTIVE
Patient switching of prescription drug brands within a therapeutic class has become more prevalent with tiered drug plan formularies. Although switching from more expensive brand name drugs to generic equivalents may reduce aggregate prescription costs, therapeutic benefit may be compromised if the patient is not switched to a drug with an equivalent therapeutic profile. This study examined whether patients switching from branded atorvastatin to either a branded or generic simvastatin were prescribed a therapeutically equivalent or higher dose, as opposed to a lower therapeutic dose.


METHODS
Study patients were selected from a national longitudinal database of 1.4 billion annual prescription drug claims. All patients active in the database during the study period (9/01/2005 to 9/30/2006) with a prescription drug claim for atorvastatin in the index month (9/2005) were selected. The 453,409 patients in the study period were followed for 12 months to determine the percent switching to simvastatin and their relative therapeutic doses after switching. Patients switching to the same or lower milligram dose of simvastatin were classified as receiving a lower therapeutic dose compared with their atorvastatin dosing.


RESULTS
Among patients using atorvastatin at the beginning of the study, 13,530 (3%) switched to simvastatin by the end of the study period. Medication changes resulted in a lower therapeutic dose in 38% of the switches. The percent of switches resulting in a lower therapeutic dose were 18% for those switching from 10 mg, 43% for those switching from 20 mg, 73% for those switching from 40 mg, and 100% for those switching from 80 mg.


CONCLUSIONS
A significant proportion of patients switching from atorvastatin to simvastatin received a lower therapeutic dose, which may have an adverse impact on patients' quality of care and health status. Further research is needed to assess the potential negative effect on patient outcomes.
Hess
Gregory
G
Surveillance Data Inc.
Sanders
Kafi N
KN
Hill
Jerrold
J
Liu
Larry Z
LZ
D000069059:Atorvastatin; D016568:Drugs, Generic / Q000008:administration & dosage* / Q000493:pharmacokinetics; D006538:Heptanoic Acids / Q000008:administration & dosage* / Q000493:pharmacokinetics; D006801:Humans; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors / Q000008:administration & dosage* / Q000493:pharmacokinetics; D011758:Pyrroles / Q000008:administration & dosage* / Q000493:pharmacokinetics; D011787:Quality of Health Care; D012189:Retrospective Studies; D019821:Simvastatin / Q000008:administration & dosage* / Q000493:pharmacokinetics; D013810:Therapeutic Equivalency; D014481:United States
D016568:Drugs, Generic; D006538:Heptanoic Acids; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D011758:Pyrroles; D000069059:Atorvastatin; D019821:Simvastatin