Horizon Pharma is buying Crealta Holdings LLC for $510 million in cash, deepening its commitment to people who need treatments for rare conditions.

The buyout comes a month after Horizon dropped its hostile bid for rival drugmaker Depomed.

Horizon, based in Dublin, makes the rheumatoid arthritis drug Duexis. It also makes the drug Actimmune, which treats a genetic condition affecting the immune system.

Crealta makes the chronic refractory gout drug Krystexxa. The condition affects about 50,000 people in the U.S. and the drug has been used to treat between 4,000 and 5,000 people since its approval in 2010.

The deal is expected to close during the first quarter.

Shares of Horizon Pharma PLC fell $1.28, or 6.3 percent, to $19.12.