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The SARfaris: GPCR, Kinase, ADME

Tuesday, 10 November 2009

New Drug Approvals - Pt. XXI - Ofatumumab (Arzerra)

The latest approval this month, on October 26th, was Ofatumumab (trade name Arzerra). Ofatumumab is a CD20-directed cytolytic monoclonal antibody indicated for the treatment of patients with refractory chronic lymphocytic leukemia (CLL) who have inadequately responded to both Fludarabine and Alemtuzumab. CLL is characterized by an abnormal proliferation of lymphocytes so-called B-cells. B-cells originate in the bone marrow and are involved in fighting infection. In CLL, the DNA of a B-cell is damaged and so it can not produce antibodies in order to fight infection. Moreover, they grow out of control and accumulate in the bone marrow and blood.

Ofatumumab is an IgG1k human monoclonal antibody which binds specifically to both the small and large extracellular loops of CD20. CD20 is a non-glycosylated phosphoprotein expressed on normal B lymphocytes and on B-cell CLL. Since it is not shed from the cell surface, it allows for antibody binding, and when so, it sends a signal across the membrane to control growth and trigger death of certain tumor cells. The Fab domain of Ofatumumab binds to the CD20 molecule, whereas the Fc domain mediates immune effector functions that result in B-cell lysis.
Ofatumumab has a molecular weight of ca. 149 kDa. The dosing is typically 12 doses administered as an initial 300mg dose, followed 1 week later by a 2,000mg dose weekly for 7 doses, followed 4 weeks later by a further 2,000 mg every 4 weeks for 4 doses (a 2g dose is equivalent to ca. 134umol). It has a volume of distribution ranging from 1.7 L to 5.1 L and its elimination occurs through both a target-independent route and a B-cell mediated route. Ofatumumab clearance is approximately 0.01 L/hr and mean half-life is ca. 14 days. The recommended dosage and full prescribing information can be found here.

<DRUG_NAME="Ofatumumab" TRADEMARK_NAME="Arzerra">
The license holder is GlaxoSmithKline and the product website is

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