Sanofi and Isis Pharmaceuticals Inc. (ISIS) won U.S. marketing approval for their drug to treat a hyper form of high cholesterol that will carry a warning label about the risk of liver toxicity.

The Food and Drug Administration cleared the injection Kynamro for people with a rare disease that leads to life- threatening high cholesterol, the agency said yesterday in a statement. People with the disease, known as homozygous familial hypercholesterolemia, may have heart attacks or die early.

The drug may generate 300 million euros ($403 million) in peak sales by 2020, Philippe Lanone, an analyst with Natixis Securities, said in an interview. The approval triggers a $25 million milestone payment to Carlsbad, California-based Isis and the company will get 30 percent to 50 percent of Kynamro profits, according to a 2008 agreement with Paris-based Sanofi.

“FDA approval of Kynamro is great news for patients with HoFH who are in need of additional treatment options for this rare, and often underdiagnosed disease,” David Meeker, the president and chief executive officer of Sanofi (SAN)’s Genzyme unit in Cambridge, Massachusetts, said in a statement.

Aegerion Pharmaceuticals Inc. (AEGR) won U.S. approval Dec. 24 for a similar medicine, Juxtapid, in pill form.

The FDA is requiring four postmarketing studies for Kynamro, including programs to monitor the safety of the drug.

Rare Disease

In late-stage trials, 8 percent of patients treated with Kynamro experienced elevated levels of an enzyme that indicates liver damage. Juxtapid from Cambridge, Massachusetts-based Aegerion also was approved with a boxed warning about the potential for liver toxicity.

Kynamro treats homozygous familial hypercholesterolemia, which causes abnormalities in liver cells responsible for clearing LDL, or low density lipoprotein, particles from the blood. People with the disease can have cholesterol levels two to four times higher than normal, according to the National Institutes of Health.

Kynamro failed to win European Union backing in December. The medicine was rejected because it leads to flu-like symptoms and liver damage that deter patients from sticking with treatment, the European Medicines Agency said in a Dec. 13 statement. Sanofi said the companies planned to request a re- examination of the opinion.

Isis studied 261 people treated with Kynamro in three pooled late-stage trials, including those with other forms of familial hypercholesterolemia, that supported a pivotal trial of 51 homozygous familial hypercholesterolemia patients.

Isis said the drug reduced LDL cholesterol by 25 percent in patients with homozygous familial hypercholesterolemia in two late-stage trials, compared with 3.3 percent for those on placebo.

The treatment may generate $50 million in 2016 for Isis, according to the average of four analysts’ estimates compiled by Bloomberg