In contrast to rituximab, which is a classic type I CD20 antibody, obinutuzumab binds to type II CD20 antibodies. This allows obinutuzumab to have a much higher induction of antibody-dependant cytotoxicity and a higher direct cytotoxic effect than the classic CD20 antibodies.
Obinutuzumab is more potent than rituximab in depleting B-cells, antitumor activity, and tumor regression.
Obinutuzumab is not metabolized by the liver.
The most serious toxicities observed with obinutuzumab are Hepatitis B virus (HBV) reactivation and progressive multifocal leukoencephalopathy (PML). HBV reactivation can occur with all anti-CD20 antibodies and can result in hepatic failure, fulminant hepatitis, and death. PML occurs as a result of JC virus infection and can be fatal as well. Other common but less serious adverse reactions include infusion reactions (pre-treat with glucocorticoids, acetaminophen, and anti-histamine to prevent this), neutropenia, thrombocytopenia, and Tumor Lysis Syndrome (TLS) (pre-treat patients, especially with a high lymphocyte count and/or a high tumor burden, with anti-hyperuricemics and hydration). It is also recommended to NOT administer live virus vaccinations prior to or during obinutuzumab treatment.