OBJECTIVES: To assess price changes with time following launch for Medicare part B injectable, generic drugs and to understand how drug characteristics influence price trajectories. METHODS: We included all Medicare part B drugs that were reported in both 2006 and 2016. Vaccines, biologics, oral agents and inhalers were excluded. Patent expiration dates were attached using the Medicare Drug Patent Expiration engine and drugs with a patent expiration date later than 2006 were removed. We used the Anatomical Therapeutic Chemical (ACT) code for each drug to identify an indication. For each drug we extracted the Average Sales Price (ASP) history from October 2006 to October 2016, published by the Center for Medicare and Medicaid services (CMS). US inflation rates were obtained from the United States Department of Labor, and prices were adjusted for inflation. For each drug we calculated the cumulative ASP change during the follow-up period. Data was analyzed using IBM SPSS Statistics software. RESULTS: We identified 166 injectable, generic drugs that fulfilled our inclusion and exclusion criteria. During our follow-up period 56 (34%) drugs had increases in price of more than 100% and 13 (8%) had increases of more than 1000%. The most common indications in the group of drugs with price increases were nervous system (25%) and anti-infectives (14%). When analyzing the price trajectory of the top increasing drugs, we found both gradual price increases and price hikes. There was no association between drug indications and price trajectory patterns. CONCLUSIONS: Generic drug costs may change substantially throughout time. Gradual price increases or acute price hikes may be due to the lack of generic substitution in the market or competitor substitution shortages due to quality, production and marketing reasons. New regulations may be needed to prevent further increases in generic drug costs.