Shares of Avanir Pharmaceuticals soared Monday after the company reported positive clinical trial results for a drug that is designed to treat agitation in Alzheimer’s disease patients.

The company said patients who were treated with AVP-923 were less agitated than patients given a placebo. The mid-stage clinical study lasted 10 weeks and included 220 patients, and the patients were evaluated with a questionnaire used to measure disturbance in patients with dementia.

Avanir stock climbed $5.24, or 78 percent, to $11.98 in afternoon trading. Earlier the stock set an eight-year high of $12.10.

Avanir says large numbers of Alzheimer’s disease patients develop behavioral and psychiatric symptoms. About 5.4 million Americans have the disease, and that number is expected to climb as the population ages. There is no cure for the disease and current drugs can only temporarily ease its symptoms.

Avanir Pharmaceuticals Inc. gets most of its revenue from a drug called Nuedexta, which is used to treat a condition called pseudobulbar affect. The ailment is associated with brain disease or injury that involves involuntary emotional outbursts such as laughing or crying. Avanir reported $26.5 million in revenue from Nuedexta during the second quarter. The Aliso Viejo, California, company also receives royalty payments on sales of Abreva, a treatment for coldsores.