ApoB antisense inhibitors are complementary oligonucleotides that are designed to directly inhibit protein synthesis by binding to messenger RNA of the target protein.  Apolipoprotein B (ApoB) is a structural component of the low-density lipoproteins, including LDL.  Mipomersen is a second generation antisense oligonucleotide that inhibits the synthesis of ApoB.  In phase III trials, addition of mipomersen to conventional lipid lowering therapy lowered median LDL-C by 24.7% from baseline compared to 3.3% for placebo.

The most common adverse effects in the patients receiving mipomersen were injection site reactions (in as many as 76%), with an increase in alanine aminotransferase >3 the upper limit of normal (ULN) in 12% of patients.

The principal limitations of this study were that only one dose of the drug was used, and hepatic fat was measured only in patients with elevations of liver function test - and those were the patients with increases of >3 X ULN.