Liberman Joshua N, Roebuck M Christopher
CVS Caremark, 11311 McCormick Rd., Hunt Valley, MD 21031, USA.
J Manag Care Pharm. 2010 Sep;16(7):502-6. doi: 10.18553/jmcp.2010.16.7.502.
The generic dispensing ratio (GDR)-the number of generic fills divided by the total number of prescriptions-is a standard performance metric on which pharmacy benefit designs and their managers are routinely evaluated. Higher GDRs are considered important because they consistently produce lower prescription drug costs.
To (a) quantify the relationship between GDR and gross pharmacy expenditures and (b) distinguish pharmacy cost savings realized from brand-to-generic conversion from those due to brand drug utilization decreases.
This study was a longitudinal, retrospective analysis of paid pharmacy claims and insurance eligibility information for 548 employers covering nearly 14 million members. Data were from the period January 1, 2007, through December 31, 2009, aggregated quarterly. In a linear fixed effects model controlling for plan membership demographics and time trends, percentage changes in gross pharmacy expenditures per member per quarter (PMPQ) were associated with changes in GDR. A second model estimated the association of GDR with gross pharmacy cost, holding total drug utilization constant. All claims counts were adjusted to 30-day equivalents, and expenditures were log--transformed.
Mean generic claims PMPQ increased by 18.4% during the study period, from 2.01 in 2007 Q1 to 2.38 in 2009 Q4. Conversely, brand claims PMPQ decreased by 21.0%, from 1.76 in 2007 Q1 to 1.39 in 2009 Q4. As a result, mean GDR per plan increased by 9.8 percentage points or a relative change of 18.2%, from 53.9% in 2007 Q1 to 63.7% in 2009 Q4. Over the 3 years, average gross pharmacy costs PMPQ increased by 14.0% from $242 to $276. The relationship between GDR and gross pharmacy expenditures, estimated in the linear fixed effects multivariate models, varied depending upon whether or not total utilization was controlled. In the first model, which did not control for total utilization, each percentage point increase in GDR was associated with a 2.5% reduction in gross pharmacy expenditure. Holding total utilization constant, the reduction in gross pharmacy expenditure for each percentage point increase in GDR was 1.3%.
Prescription drug cost savings are realized with increases in GDR. During 2007-2009, each 1 percentage point increase in GDR was associated with a drop of 2.5% in gross pharmacy expenditures. Slightly more than one-half of the savings was derived from the lower drug prices enjoyed with brand-to-generic conversions. The remaining savings, however, were attributed to reduced brand drug utilization. Pharmacy benefit managers and plan sponsors should exercise care to ensure that increases in GDR do not represent reductions in appropriate medication use.
通用配药比例（GDR）——通用药品配药数量除以处方总数——是一项标准的绩效指标，药房福利设计及其管理者通常据此接受评估。较高的GDR被认为很重要，因为它们能持续降低处方药成本。
（a）量化GDR与药房总支出之间的关系，以及（b）区分从品牌药转换为通用药所实现的药房成本节省与因品牌药使用量减少而实现的成本节省。
本研究是对548家雇主的已支付药房理赔和保险资格信息进行的纵向回顾性分析，这些雇主覆盖近1400万成员。数据来自2007年1月1日至2009年12月31日期间，按季度汇总。在一个控制计划成员人口统计学特征和时间趋势的线性固定效应模型中，每季度每位成员的药房总支出（PMPQ）的百分比变化与GDR的变化相关。第二个模型估计了GDR与药房总成本之间的关联，同时保持总药物使用量不变。所有理赔计数均调整为30天等效值，支出进行对数转换。
在研究期间，通用药品理赔的平均PMPQ增长了18.4%，从2007年第一季度的2.01增至2009年第四季度的2.38。相反，品牌药理赔的PMPQ下降了21.0%，从2007年第一季度的1.76降至2009年第四季度的1.39。结果，每个计划的平均GDR提高了9.8个百分点，相对变化为18.2%，从2007年第一季度的53.9%升至2009年第四季度的63.7%。在这3年中，平均药房总成本PMPQ从242美元增至276美元，增长了14.0%。在控制总使用量与否的情况下，线性固定效应多变量模型中估计的GDR与药房总支出之间的关系有所不同。在未控制总使用量的第一个模型中，GDR每增加1个百分点，药房总支出就会减少2.5%。在保持总使用量不变的情况下，GDR每增加1个百分点，药房总支出的减少幅度为1.3%。
随着GDR的提高，实现了处方药成本的节省。在2007 - 2009年期间，GDR每增加1个百分点，药房总支出就会下降2.5%。略多于一半的节省来自品牌药转换为通用药后享受到的较低药品价格。然而，其余的节省归因于品牌药使用量的减少。药房福利管理者和计划赞助商应谨慎行事，以确保GDR的提高并不意味着适当药物使用的减少。
