15. Namenda XR

Allergan's Namenda XR started facing generic competition in February. (Allergan)

Namenda XR 
Company: Allergan 
2017 U.S. sales: $452 million 
Disease: Dementia 
Generic launch: Feb. 21 

Rounding out this year's list of top patent expirations is Allergan's Namenda XR, a drug that made headlines back in 2015 when its predecessor formula went generic. The drug treats dementia associated with Alzheimer's disease, and as of February, it has faced copycat rivals. 

Allergan ran into some legal pushback back in 2015 when it tried to do a "hard switch" to the long-acting version to keep as many patients as possible in the Allergan fold. The older version's patent expiration was nearing, and Allergan figured that pulling that formula off the market would force patients to switch to the patent-protected extended-release version. It was a bid to maintain market share, but a court ultimately shot down that strategy. 

More recently, Namenda XR turned in $452 million in U.S. sales last year, Allergan reported—just enough to make the No. 15 spot in the top 2018 patent expirations, but a 28% drop versus the prior year. The original version of Namenda had to contend against generics, which dented sales for the follow-up brand.  

RELATED: Allergan, shut down on Namenda hard switch, takes it up with SCOTUS 

Meanwhile, the company is hoping follow-up combo drug Namzaric can pick up where its Namenda products left off. The newer drug marries Namenda's active ingredient with Eisai's Aricept, but has so far been slow to take off. Last year, it generated $130 million in sales. 

Amneal launched its generic version of Namenda XR on Feb. 21, according to a press release. Lupin, Mylan and other generic drugmakers have FDA-approved copycats, according to the agency. 

Aside from its products Restasis and Namenda included in this report, Allergan also expects to face new generic competition on Estrace Cream and ulcerative colitis drug Delzicol this year, executives recently said. Estrace brought in $366 million in the U.S. last year, while Delzicol was one of a pair of UC drugs that generated $195 million. Together, patent losses represent more than $2.2 billion in sales under threat this year. 

15. Namenda XR