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7/1/2003

Radioimmunotherapy Approved for Certain Lymphomas

Cheryl A. Thompson

Bexxar (PDF), a two-step regimen involving a ready-to-administer radioisotope of iodine and a monoclonal antibody specific to an antigen on certain non-Hodgkin's lymphoma cells, has been approved by the Food and Drug Administration, according to an announcement Monday by Corixa Corp. and GlaxoSmithKline, who will jointly market the new product.

The regimen is indicated for patients with follicular lymphoma whose affected cells bear the antigen CD20 and whose disease has not responded to rituximab therapy—itself a second-line treatment—or has progressed after initially responding to rituximab therapy.

According to Bexxar's labeling, the goal of step 1 in the regimen is to determine how well the combination of radioactive iodine and antibody, known as tositumomab, distributes through a patient's body and then leaves. The goal of step 2, undertaken seven to 14 days after step 1, is to expose the lymphoma cells to enough iodine I 131 tositumomab to kill them but spare as many normal blood cells as possible. Each step involves first administering tositumomab into the patient's vein over one hour, longer if "infusional" toxicity—fever, chills, sweating, hypotension, breathing difficulties, bronchospasm, and nausea—develops. The entire course of treatment consists of one time through this two-step regimen.

Patients with a hypersensitivity to rodent proteins must not receive tositumomab because part of the antibody is based on a murine structure.

During clinical studies of the regimen, life-threatening decreases in the numbers of white blood cells, red blood cells, and platelets were the most commonly found adverse reactions in patients after they received the therapeutic portion, delivered in step 2. Weakness, fever, nausea, infection, or cough developed in at least 20 percent of patients, according to the product's labeling.

The dosing schedule in the labeling calls for patients to receive a thyroid-protective agent—saturated solution of potassium iodide, Lugol's solution, or potassium iodide tablets—starting at least 24 hours before the first dose of iodine I 131 tositumomab and continuing through two weeks after the second dose. Also, all patients should receive 650 mg of actaminophen and 50 mg of diphenhydramine orally 30 minutes before receiving tositumomab in steps 1 and 2.

Corixa and GlaxoSmithKline said Bexxar will be sold only to nuclear pharmacies, oncologists, and nuclear medicine physicians at sites that have completed the training program in calculating and administering doses. Training can be requested and orders placed at 877-423-9927, 8 a.m. to 6 p.m. EST.

Corixa said it hopes to start supplying Bexxar to cancer treatment centers in about 30 days.Vials of the regimen's components will be shipped from different sites: tositumomab from McKesson BioServices in Maryland, and iodine I 131 tositumomab from MDS Nordion in Canada.