Isis Cholesterol Drug Effective, but Safety a Worry: BioBuzz

CARLSBAD, Calif. (TheStreet) -- An experimental drug from Isis Pharmaceuticals(ISIS Quote) and Genzyme(GENZ Quote) cut levels of "bad" LDL cholesterol by 25% in patients with a rare genetic disorder that causes extremely high and dangerous levels of cholesterol, according to data presented today at a medical meeting.

But the drug, known as mipomersen, also caused elevated liver enzymes in 12% of patients -- a signal that the drug may have damaging effects on the liver.

Investor worries over the drug's safety sent Isis shares lower.

The pivotal, phase III study of mipomersen met its primary endpoint by reducing levels of LDL cholesterol by 25% compared to a 3% reduction after treatment with a placebo. Mipomersen lowered cholesterol level on top of standard therapy involving statin drugs.

The 34 patients in the study suffer from homozygous familial hypercholesterolemia (HoFH), an extremely rare genetic condition in which a gene responsible for the removal of cholesterol from the body is missing. Patients with HoFH have extremely high cholesterol levels and are at high risk for heart attack and early death.

Mipomersen is an injectable drug that blocks a protein responsible for delivering LDL cholesterol throughout the body.

But four of 34 or patients in the study, or 12%, experienced elevated liver enzyme levels three times higher than normal. Liver enzyme elevations in three of these patients reached five to eight times normal. One of these patients dropped out of the study due to the liver toxicity.

Genzyme and Isis said none of these patients exhibited any permanent signs of liver damage and all liver tests returned to normal when patients stopped taking mipomersen.