There are several types of pharmaceutical competition. In addition to competition among producers of the same chemical substance (“within-substance competition”), there may be competition among producers of different chemical substances in the same chemical subgroup (“between-substance competition”). There have been numerous econometric studies of the effect of within-substance competition on drug prices, but empirical evidence about the effect of between-substance competition is far more limited. The primary objective of this study is to assess the impact of the entry of new drugs in a drug's therapeutic class on branded drug prices, generic drug prices, and the generic market share, using publicly-available US data for the period 1997–2017. Two methods are used to estimate the effects of between-substance and within-substance competition on those variables. The first method is standard 2-way fixed effects estimation based on aggregate data. The second method, based on micro data, is estimation using the DID_MULTIPLEGT procedure developed by de Chaisemartin et al. (2021), which does not rely on, and allows us to test for, “parallel trends.” Between-substance competition does not appear to have any effect on brand-name drug prices, although our inability to fully account for rebates may bias the estimates towards zero. (There is also little evidence for an effect of within-substance competition on brand-name drug prices.) However, between-substance competition has a significant negative effect on generic drug prices. We estimate that the 1985–2005 increase in the number of substances ever registered in a drug's ATC4 chemical subgroup reduced the 2017 price of generic drugs by 42%. (The ratio of the generic-price reduction attributable to rising between-substance competition to the generic-price reduction attributable to rising within-substance competition also happens to be 42%.) A striking finding is that the entry of imitators has no effect on the prices of brand-name drugs, but the entry of innovators has a significant negative effect on the prices of generic drugs in the same ATC4 chemical subgroup. In addition, between-substance competition has a significant positive effect on the generic market share: the 1985–2005 increase in the number of substances ever registered in a drug's ATC4 chemical subgroup increased the 2017 generic market share by 15.0 percentage points. Due to its effects on generic drug prices and the generic market share, the 1985–2005 increase in between-substance competition reduced the average 2017 price of drugs that were already sold in 1997 by 35%. We estimate that 36% of 2017 expenditure on drugs that were first registered during 1986–2005 was offset by reduced 2017 expenditure on drugs that were sold in both 1997 and 2017.

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药品价格是否受到创造性破坏？来自美国的证据，1997-2017

有几种类型的制药竞争。除了同一化学物质的生产者之间的竞争（“物质内竞争”）外，同一化学亚组中不同化学物质的生产者之间可能存在竞争（“物质间竞争”）。已经有大量关于物质内竞争对药品价格影响的计量经济学研究，但关于物质间竞争影响的经验证据要有限得多。本研究的主要目的是使用 1997 年至 2017 年期间公开可用的美国数据，评估新药进入药物治疗类别对品牌药价格、仿制药价格和仿制药市场份额的影响。使用两种方法来估计物质间和物质内竞争对这些变量的影响。第一种方法是基于聚合数据的标准双向固定效应估计。第二种方法，基于微数据，是使用 de Chaisemartin 等人开发的 DID_MULTIPLEGT 程序进行估计。(2021)，它不依赖并允许我们测试“平行趋势”。物质之间的竞争似乎对品牌药价格没有任何影响，尽管我们无法完全考虑回扣可能会使估计偏向零。（也几乎没有证据表明物质内竞争对品牌药价格有影响。）然而，物质间竞争对仿制药价格有显着的负面影响。我们估计，1985-2005 年药物 ATC4 化学亚组中注册的物质数量增加，使 2017 年仿制药价格下降了 42%。（物质间竞争加剧导致的仿制药降价与物质内竞争加剧导致的仿制药降价的比率也恰好是 42%。）一个惊人的发现是，模仿者的进入对品牌药的价格，但创新者的进入对同一 ATC4 化学亚组的仿制药价格有显着的负面影响。此外，物质间竞争对仿制药市场份额有显着的积极影响：1985 年至 2005 年，药品中注册的物质数量有所增加。s ATC4 化学子组将 2017 年仿制药市场份额提高了 15.0 个百分点。由于其对仿制药价格和仿制药市场份额的影响，1985-2005 年物质间竞争的增加使 1997 年已售出的药物 2017 年平均价格降低了 35%。我们估计，2017 年 36% 的 1986-2005 年首次注册药物支出被 2017 年 1997 年和 2017 年销售的药物支出减少所抵消。