By Caroline Humer

Dec 22 (Reuters) - The nation's largest pharmacy benefit manager has lined up a cheaper price from AbbVie Inc on its newly approved hepatitis C treatment and, in most cases, will no longer cover Gilead Sciences Inc treatments, Express Scripts said on Monday.

Express Scripts has opposed the $84,000 pricetag of Gilead Sciences' Sovaldi treatment since it was approved a year ago, saying that was unaffordable. The $1,000 a day pill opened a national debate about drug prices and increased insurer pressure on drug makers to cut prices.

AbbVie, whose Viekira Pak drug was approved on Friday by U.S. regulators, has set a significantly lower price, Express Scripts Chief Medical Officer Steve Miller said in an interview.

The pricing agreement covers Express Scripts' National Preferred Formulary, a list of approved and covered drugs that applies to 25 million Americans with its pharmacy insurance.

"This is unprecedented," Miller said, explaining that specialty drugs of this type typically are priced right next to each other.

Express Scripts declined to say how much it would pay for the AbbVie drug, which it will sell only through its by-mail Accredo specialty pharmacy. It lists for $83,319 for a 12-week treatment and is also indicated for a 24-week treatment for some patients. Drug makers typically discount drugs in the United States by 10 to 20 percent.

Miller said that the AbbVie price was narrowing the gap towards the lower prices that Western European countries have negotiated for their citizens for Sovaldi. They run from $51,373 in France to $66,000 in Germany.

The AbbVie regimen consists of four different anti-viral drugs to be taken as three pills in the morning and one in the evening. The U.S. Food and Drug Administration approved the regimen for patients with genotype 1 form of the virus, the most common type of hepatitis C and the most difficult to treat.

Express Scripts said that starting Jan. 1, 2015, it would only pay for the AbbVie drug for patients who have genotype 1. Express Scripts will no longer cover Harvoni, a one-pill treatment for patients with genotype 1 that costs $94,500 for a 12-week course.

It will cover Sovaldi in cases where patients have other types of the disease.

Express Scripts said patients with both early and late forms of the disease will also be reimbursed for the AbbVie drug.

(Reporting by Caroline Humer; Editing by Diane Craft)