Novartis AG and Shire Plc are among drugmakers weighing offers for Belgian eye-medicine company ThromboGenics NV, people familiar with the matter said. Novartis, which is based in Basel, Switzerland, is considered the most likely buyer because it already has a partnership to market ThromboGenics’s Jetrea eye medicine outside of the U.S., the people said, asking not to be identified because the process is private. The sale may value the company at as much as $1.3 billion, one of the people said. Shire, a maker of drugs for rare genetic diseases, is among potential bidders that include Roche Holding AG, Valeant Pharmaceuticals International Inc., Regeneron Pharmaceuticals Inc. and Allergan Inc., two of the people said. Non-binding offers are due at the end of the month, one of the people said. ThromboGenics had a record gain on Feb. 24, when the drugmaker said it hired Morgan Stanley to explore strategic options. Jetrea’s sales have missed the company’s forecasts and the shares have lost half their value in the past 12 months, valuing the company at about 661.2 million euros ($915 million). Representatives for ThromboGenics, Dublin-based Shire, Novartis, Valeant, Allergan and Roche declined to comment. Tarrytown, New York-based Regeneron couldn’t be immediately reached for comment. Best-Selling Drug ThromboGenics’s best-selling treatment is Jetrea, an injection to treat a vision-destroying condition called vitreomacular adhesion that was previously treated with surgery. Almost 7,000 patients had been treated with Jetrea in the U.S. since the drug reached the market in January 2013, the company said in the February statement. Novartis holds the rights to Jetrea outside of the U.S. and pays ThromboGenics royalties for sales it generates in those markets. Novartis and Roche, also based in Basel, have a marketing partnership on another eye drug, Lucentis, which is used for wet age-related macular degeneration. Shire Chief Executive Officer Flemming Ornskov is expanding into eye diseases to help the company move beyond products for attention deficit hyperactivity disorder and rare illnesses. Last year, Shire acquired eye-drug maker SARcode Bioscience Inc. for at least $160 million as well as Sweden’s Premacure AB to gain an experimental treatment against a blindness-causing disorder in babies born prematurely.