Astellas Pharma Inc. is suing Xellia Pharmaceuticals ApS, saying Xellia’s proposed copycat of the injectable antifungal drug would infringe an Astellas patent.

Astellas is seeking a court order blocking copies until the patent has expired, according to a complaint filed Nov. 19 in the U.S. District Court for the District of Delaware.

Mycamine is used to treat Candida fungal infections in adults and children and to prevent Candida infections in patients undergoing stem-cell transplants. Astellas’ patent expires in January 2021, according to complaint.

Mycamine/Funguard had global sales of 41 billion yen ($364 million), 3.2% of revenue, in the 12 months...