Drug and medical cost effects of a drug formulary change with therapeutic interchange for statin drugs in a multistate managed Medicaid organization.

OBJECTIVE: Therapeutic interchange (TI) interventions are commonly used to manage pharmacy benefit costs. While several studies have considered the effect that TI interventions have on drug costs, most have not considered the effect they have on medical management costs. The purpose of the present study was to assess drug cost and drug therapy management costs of a TI intervention following a change in the drug formulary for 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor (statin) drugs, including the conversion of atorvastatin from formulary to nonformulary status.
METHODS: A retrospective, quasi-experimental within-subjects design was used in this study. Administrative claims data were obtained from a select northeastern segment of a multistate Medicaid managed care organization (MCO). To be included in the study, patients had to meet the following criteria: (1) they must have had a minimum of 3 atorvastatin prescriptions during a 6-month enrollment phase, (2) they must have been continuously enrolled throughout the 900-day study period, and (3) they must have switched from atorvastatin to another statin between April 1, 2003, and July 31, 2003. The day of the switch from atorvastatin marked for each patient the end of the 12-month pre-TI period and the beginning of the 12-month post-TI period. Two separate dependent variables were developed: (1) statin drug costs (statin cost + dispensing fee) and (2) the costs paid by the MCO for the medical management of statin therapy, including office visit costs and the medical laboratory costs of measuring lipids and creatine kinase, and of checking liver functions. To estimate expenditures over 24 months, a panel analytic technique was used that allows each patient to serve as his or her own control. Multivariate models were used to assess the effects of the TI policy while controlling for age, gender, adjunctive dyslipidemia therapy, comorbidity, presence of a prior coronary artery event, statin compliance, cardiologist management, and disease severity.
RESULTS: Of the 3,636 patients who met the study inclusion criteria and were converted from atorvastatin to an alternate statin drug, 129 patients (3.5%) switched back to atorvastatin following the TI. The average statin cost per claim in the 12-month post-TI period was Dollars 70.93, 9.5% less than the average cost in the 12-month pre-TI period (Dollars 78.40). The average cost per patient per year (PPPY) for statin laboratory tests (lipid panels, creatine kinase tests, and liver function tests) increased by 31.5% to Dollars 16.15 in the post-TI period compared with Dollars 12.28 PPPY in the pre-TI period, and medical office visit costs increased by 44.9% to Dollars 20.70 PPPY in the post-TI period compared with Dollars 14.29 PPPY in the preperiod. These increased costs related to the medical management of statin therapy were overwhelmed by an 11.7% reduction in statin drug costs, from Dollars 793.69 PPPY in the pre-TI period to Dollars 701.01 PPPY in the post-TI period, resulting in a net 10.0% reduction for combined statin costs and related medical costs, from Dollars 820.27 PPPY in the pre-TI period to Dollars 737.87 in the post-TI period. After limiting the analysis to patients who did not convert from atorvastatin to pravastatin (which cost more than atorvastatin before the rebate) and controlling for the influence of potential confounders, statin expenditure decreased by 33% (P < 0.001). Multivariate models indicated no statistically significant differences in the costs related to the medical management of statin therapy after the TI compared with before the TI.