Stop Drug Companies from Overcharging Seniors in Medicare Part B Act of 2019 This bill requires manufacturers of covered drugs under Medicare medical services to issue rebates to the Centers for Medicare & Medicaid Services. Rebates are calculated based on the number of units sold and the amount by which the manufacturer price exceeds inflation. The bill's requirements do not apply to drugs that cost less than $100 annually per user in 2020 (and as adjusted for inflation annually thereafter) or to drugs on a specified drug shortage list. The bill also eliminates cost-sharing for such drugs for beneficiaries whose out-of-pocket costs meet or exceed a specified threshold.