The drugmaker Horizon Pharma says it is questioning its relationship with an Express Scripts business after the U.S. pharmacy benefits giant sued Horizon for about $140 million and dumped a pharmacy that dispenses its drugs.

The drugmaker Horizon Pharma says it is questioning its relationship with an Express Scripts business after the U.S. pharmacy benefits giant sued Horizon for about $140 million and dumped a pharmacy that dispenses its drugs.

Shares of Horizon Pharma Plc are down more than 17 percent in premarket trading Wednesday. The Dublin company said Express Scripts is trying to squeeze out small pharmacies that compete with its own specialty business, Accredo.

Horizon says it will re-evaluate its relationship with Accredo, which accounts for a bigger slice of its revenue than any other pharmacy.

Express Scripts Holding Co. says customers have many choices for getting medicine, and it takes action when pharmacies fall out of compliance with network agreements. It also says Horizon isn't sticking to a contract with Express Scripts over rebate agreements.