Nov 7 (Reuters) - Shares of Mallinckrodt Plc were down about 9 percent in premarket trading on Tuesday after the drugmaker reported lower-than-expected quarterly revenue, hurt mainly by weak sales of its Acthar drug.
Acthar gel, which is used to treat infantile spasms and multiple sclerosis, brought in sales of $308.7 million, missing consensus estimate of $326.6 million, according to Stifel.
Mallinckrodt has been under pressure as it faces scrutiny over the pricey gel, while its respiratory treatment Inomax faces looming competition after a ruling invalidated some of the drug's patents in September.
The company also warned that Acthar sales are likely to fall sequentially in the fourth quarter.
Total net sales were $739.9 million in the third quarter ended Sept. 30, missing analysts' estimates of $811.9 million, according to Thomson Reuters I/B/E/S.
Shares of the company were down 8.6 percent at $28.45 in premarket trading. The stock has been down about 37 percent this year. (Reporting by Manas Mishra in Bengaluru; Editing by Anil D'Silva)