(Reuters) -AbbVie shares rose 4% to a record high on Thursday after the U.S. drugmaker said it expected no generic competition for its blockbuster immunology drug Rinvoq until 2037, a four-year extension, according to some analysts.

Rinvoq, used for the treatment of rheumatoid arthritis and other autoimmune diseases, is AbbVie's second best-selling drug behind Skyrizi.

The company has been doubling down on the immunology treatments to counter the drop in sales of arthritis treatment Humira, its once bestselling drug that is battling competition from several cheaper biosimilars in the U.S. since 2023.

The settlement with some generic drugmakers, which is subject to certain provisions, is expected to prevent sales erosion of Rinvoq from generic competitors until April 2037.

J.P. Morgan analyst Chris Schott said the extension gives AbbVie "several more years of runway on one of its key growth drivers", providing more time to develop its experimental drugs ahead of major loss of exclusivity in the mid-2030s.

Rinvoq generated sales of $5.97 billion, or more than 10% of the company's total revenue, in 2024. Skyrizi and Rinvoq are expected to together bring in more than $31 billion in 2027, according to AbbVie.

"This is clearly a positive development, supporting longer-term protection of the Rinvoq franchise," said William Blair analyst Matt Phipps, who had previously assumed a 2033 loss of exclusivity.

Phipps assumes four additional years of exclusivity could lift AbbVie's expectation to add roughly $2 billion to peak-year sales of Rinvoq with the next wave of potential approvals.

The drug is being tested for several immune-related diseases such as alopecia areata, vitiligo, hidradenitis suppurativa and systemic lupus erythematosus.

(Reporting by Christy Santhosh in Bengaluru; Editing by Sriraj Kalluvila)