Table 2.

Medicare Part D Gross Spending and Estimated Discounts for the Top Ten Drugs, 2016

Rank	Brand name	Generic name	Medicare Part D spending	Average discount	Base-case analyses		Sensitivity analyses reducing discounts by 25%
					Estimated Part D discounts	Proportion of total Medicare Part D discounts	Estimated Part D discounts	Proportion of Total Medicare Part D discounts
1	Harvoni	Ledipasvir/sofosbuvir	$4.4Bn	66%	$2.9Bn	10%	$2.2Bn	7%
2	Lantus	Insulin glargine	$4.2Bn	54%	$2.3Bn	8%	$1.7Bn	6%
3	Humalog	Insulin lispro	$2.2Bn	70%	$1.6Bn	5%	$1.2Bn	4%
4	Novolog	Insulin aspart	$2.3Bn	67%	$1.5Bn	5%	$1.2Bn	4%
5	Advair	Fluticasone/salmeterol	$2.5Bn	56%	$1.4Bn	5%	$1.1Bn	4%
6	Januvia	Sitagliptin Phosphate	$2.4Bn	54%	$1.3Bn	5%	$1.0Bn	3%
7	Levemir	Insulin detemir	$2.0Bn	52%	$1.0Bn	4%	$0.8Bn	3%
8	Symbicort	Budesonide/formoterol	$1.4Bn	65%	$0.9Bn	3%	$0.7Bn	2%
9	Xarelto	Rivaroxaban	$2.0Bn	36%	$0.7Bn	2%	$0.5Bn	2%
10	Eliquis	Apixaban	$1.9Bn	35%	$0.7Bn	2%	$0.5Bn	2%
Total			$25.4Bn		$14.3Bn	49%	$10.7Bn	37%

As described in the “METHODS” section, gross spending was extracted from the Medicare Part D spending dashboard.⁶ Average discount data was obtained from SSR Health and includes not only rebates from manufacturers to payers but also any other manufacturer concession. Estimated Part D discounts were calculated as the product between gross spending and the average discount. The proportion of total Medicare discounts was estimated as the quotient between the estimated discount for a given drug and $29billion (total manufacturer discounts in Medicare Part D in 2016)³

None of the top 10 drugs by estimated discounts had missing data. In sensitivity analyses, we reduced estimates of discounts by 25% (relative difference). For instance, the estimated discount for Harvoni in SSR Health data was 66%. Then, we performed sensitivity analyses using 49.5% (75% of 66%) as the estimate