Background: Drug pricing and availability are key concerns for reducing health care costs and meeting patient needs. There is a complex chain of manufacturers, payers, wholesalers, retailers, patients, and other parties in drug supply and reimbursement. Understanding which of these parties drive generic manufacturer choice can inform economic models and the epidemiology of generic drug use.
Methods: US Medicare claims from 2014 for certain generic drugs were evaluated for associations between manufacturer and several other variables. We performed multinomial logistic regressions for two commonly used anticoagulants, warfarin and enoxaparin, using manufacturer as the dependent variable and pharmacy chain, county, and Medicare Part D plan provider as predictor variables. Other generic drugs were also evaluated.
Results: In 2014, the manufacturer of generic warfarin and enoxaparin received by Medicare Part D beneficiaries was strongly associated with the dispensing pharmacy chain. For prescriptions of these drugs filled at large pharmacy chains, greater than 75% of the variance in generic manufacturer was explained by the dispensing pharmacy chain. This association was durable over extended time frames and observed for other drugs with different indications.
Conclusions: Dispensing pharmacy chain is a strong driver of the manufacturer of a generic drug received by Medicare Part D beneficiaries. The effect of pharmacy chain is much larger than that of payers and geographic location. This association can inform economic models for generic competition as well as epidemiological studies on generic drug use demographics and outcomes.
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