The largest pharmacy benefit manager in the US, Express Scripts, has negotiated a cheaper price from AbbVie for its Viekira Pak hepatitis C treatment approved by the US Food and Drug Administration (FDA) on Dec. 19.

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.

In most cases, Express said, it will no longer reimburse a competitive drug made by Gilead Sciences for patients who have the genotype 1 form of the disease - which includes 70% of US patients.

While Gilead's medicines have set a new standard, curing the vast majority of patients in only 12 weeks, the high prices for hepatitis C drugs has opened a national debate in the US about drug prices altogether as well as increasing insurer pressure on drugmakers to cut prices.

Express Scripts has opposed the $84,000 price tag of Gileads' Sovaldi treatment - for the 12-week course of therapy - since it was approved a year ago, on grounds it was unaffordable. Gilead's Harvoni costs $94,500 for 12 weeks of treatment.

AbbVie said the wholesale price of Viekira Pak would be $83,319 for a typical 12-week course. That is less than the Gilead drugs, observers note, but probably not enough of a discount to allay complaints about high prices.

Nonetheless, health plans and pharmacy benefit managers generally negotiate discounts in exchange for a better positioning on the formulary, and AbbVie is believed to be prepared to offer more concessions.

Express Scripts' chief medical officer Steve Miller said the AbbVie offer narrows the gap to the lower prices Western European countries have negotiated for Sovaldi. These are said to range from $51,373 in France to $66,000 in Germany.

According to US reports, pharmacy benefit managers in the recent past have refused to pay at all for their less preferred drug. Express Scripts' national preferred formulary is said to be planning to exclude about 70 drugs in 2015, including Harvoni, Sovaldi and another new hepatitis C drug, Johnson & Johnson's Olysio.