Maasol (IBRITUMOMAB TIUXETAN)

Relapsed Or Refractory, Low-grade Or Follicular NHL

Maasol (IBRITUMOMAB TIUXETAN) is indicated for the treatment of relapsed or refractory, low-grade or follicular B-cell non-Hodgkin's lymphoma (NHL).

Previously Untreated Follicular NHL

Maasol (IBRITUMOMAB TIUXETAN) is indicated for the treatment of previously untreated follicular NHL in patients who achieve a partial or complete response to first-line chemotherapy.

Recommended Dosing Schedule

• Administer the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen as outlined in in the diagram.
• Initiate the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen following recovery of platelet counts to ≥ 150,000/mm³ at least 6 weeks, but no more than 12 weeks, following the last dose of first-line chemotherapy.
• Only administer Rituxan/Maasol (IBRITUMOMAB TIUXETAN) in facilities where immediate access to resuscitative measures is available.

Overview Of Dosing Schedule

Maasol (IBRITUMOMAB TIUXETAN) Therapeutic Regimen Dosage And Administration

Day 1

• Premedicate with acetaminophen 650 mg orally and diphenhydramine 50 mg orally prior to rituximab infusion.
• Administer rituximab 250 mg/m² intravenously at an initial rate of 50 mg/hr. In the absence of infusion reactions, escalate the infusion rate in 50 mg/hr increments every 30 minutes to a maximum of 400 mg/hr. Do not mix or dilute rituximab with other drugs.
• Immediately stop the rituximab infusion for serious infusion reactions and discontinue the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen.
• Temporarily slow or interrupt the rituximab infusion for less severe infusion reactions. If symptoms improve, continue the infusion at one-half the previous rate.

Day 7, 8 or 9

• Premedicate with acetaminophen 650 mg orally and diphenhydramine 50 mg orally prior to rituximab infusion.
• Administer rituximab 250 mg/m² intravenously at an initial rate of 100 mg/hr. Increase rate by 100 mg/hr increments at 30 minute intervals, to a maximum of 400 mg/hr, as tolerated. If infusion reactions occurred during rituximab infusion on Day 1 of treatment, administer rituximab at an initial rate of 50 mg/hr and escalate the infusion rate in 50 mg/hr increments every 30 minutes to a maximum of 400 mg/hr.
• Administer Y-90 Maasol (IBRITUMOMAB TIUXETAN) injection through a free flowing intravenous line within 4 hours following completion of rituximab infusion. Use a 0.22 micron low-protein-binding in-line filter between the syringe and the infusion port. After injection, flush the line with at least 10 mL of normal saline.
  • If platelet count ≥ 150,000/mm³, administer Y-90 Maasol (IBRITUMOMAB TIUXETAN) over 10 minutes as an intravenous injection at a dose of Y-90 0.4 mCi per kg (14.8 MBq per kg) actual body weight.
  • If platelet count ≥ 100,000 but ≤ 149,000/mm³, in relapsed or refractory patients, administer Y-90 Maasol (IBRITUMOMAB TIUXETAN) over 10 minutes as an intravenous injection at a dose of Y-90 0.3 mCi per kg (11.1 MBq per kg) actual body weight.
  • Do not administer more than 32 mCi (1184 MBq) Y-90 Maasol (IBRITUMOMAB TIUXETAN) dose regardless of the patient's body weight.
• Monitor patients closely for evidence of extravasation during the injection of Y-90 Maasol (IBRITUMOMAB TIUXETAN). Immediately stop infusion and restart in another limb if any signs or symptoms of extravasation occur.

Directions For Preparation Of Radiolabeled Y-90 Maasol (IBRITUMOMAB TIUXETAN) Doses

A clearly-labeled kit is required for preparation of Yttrium-90 (Y-90) Maasol (IBRITUMOMAB TIUXETAN). Follow the detailed instructions for the preparation of radiolabeled Maasol (IBRITUMOMAB TIUXETAN).

Required materials not supplied in the kit:

1. Yttrium-90 Chloride Sterile Solution
2. Three sterile 1 mL plastic syringes
3. One sterile 3 mL plastic syringe
4. Two sterile 10 mL plastic syringes with 18-20 G needles
5. ITLC silica gel strips
6. 0.9% Sodium Chloride aqueous solution for the chromatography solvent
7. Developing chamber for chromatography
8. Suitable radioactivity counting apparatus
9. Filter, 0.22 micrometer, low-protein-binding
10. Appropriate acrylic shielding for reaction vial and syringe for Y-90

Method

1. Allow contents of the refrigerated Y-90 Maasol (IBRITUMOMAB TIUXETAN) kit (Maasol (IBRITUMOMAB TIUXETAN) vial, 50 mM sodium acetate vial, and formulation buffer vial) to reach room temperature.
2. Place the empty reaction vial in an appropriate acrylic shield.
3. Determine the amount of each component needed:
   • Calculate volume of Y-90 Chloride equivalent to 40 mCi based on the activity concentration of the Y-90 Chloride stock.
   • The volume of 50 mM Sodium Acetate solution needed is 1.2 times the volume of Y-90 Chloride solution determined in step 3.a, above.
   • Calculate the volume of formulation buffer needed to bring the reaction vial contents to a final volume of 10 mL.
4. Transfer the calculated volume of 50 mM Sodium Acetate to the empty reaction vial. Coat the entire inner surface of the reaction vial by gentle inversion or rolling.
5. Transfer 40 mCi of Y-90 Chloride to the reaction vial using an acrylic shielded syringe. Mix the two solutions by gentle inversion or rolling.
6. Transfer 1.3 mL of Maasol (IBRITUMOMAB TIUXETAN) (ibritumomab tiuxetan) to the reaction vial. Do not shake or agitate the vial contents.
7. Allow the labeling reaction to proceed at room temperature for 5 minutes. A shorter or longer reaction time may adversely alter the final labeled product.
8. Immediately after the 5-minute incubation period, transfer the calculated volume of formulation buffer from step 3.c. to the reaction vial. Gently add the formulation buffer down the side of the reaction vial. If necessary, withdraw an equal volume of air to normalize pressure.
9. Measure the final product for total activity using a radioactivity calibration system suitable for the measurement of Y- 90.
10. Using the supplied labels, record the date and time of preparation, the total activity and volume, and the date and time of expiration, and affix these labels to the shielded reaction vial container.
11. Patient Dose: Calculate the volume required for a Y-90 Maasol (IBRITUMOMAB TIUXETAN) dose. Withdraw the required volume from the reaction vial. Assay the syringe in the dose calibrator suitable for the measurement of Y-90. The measured dose must be within 10% of the prescribed dose of Y-90 Maasol (IBRITUMOMAB TIUXETAN) and must not exceed 32 mCi (1184 MBq). Using the supplied labels, record the patient identifier, total activity and volume and the date and time of expiration, and affix these labels to the syringe and shielded unit dose container.
12. Determine Radiochemical Purity.
13. Store Yttrium-90 Maasol (IBRITUMOMAB TIUXETAN) at 2-8°C (36-46°F) until use and administer within 8 hours of radiolabeling. Immediately prior to administration, assay the syringe and contents using a radioactivity calibration system suitable for the measurement of Y-90.

Procedure For Determining Radiochemical Purity

Use the following procedures for radiolabeling Y-90 Maasol (IBRITUMOMAB TIUXETAN):

1. Place a small drop of Y-90 Maasol (IBRITUMOMAB TIUXETAN) at the origin of an ITLC silica gel strip.
2. Place the ITLC silica gel strip into a chromatography chamber with the origin at the bottom and the solvent front at the top. Allow the solvent (0.9% NaCl) to migrate at least 5 cm from the bottom of the strip. Remove the strip from the chamber and cut the strip in half. Count each half of the ITLC silica gel strip for one minute (CPM) with a suitable counting apparatus.
3. Calculate the percent RCP as follows:
   

   % RCP =	CMP bottom half	x 100
   	CPM bottom half+ CPM top half

4. Repeat the ITLC procedure if the radiochemical purity is < 95%. If repeat testing confirms that radiochemical purity is < 95%, do not administer the Y-90 Maasol (IBRITUMOMAB TIUXETAN) dose.

Radiation Dosimetry

During clinical trials with Maasol (IBRITUMOMAB TIUXETAN), estimations of radiation-absorbed doses for Y-90 Maasol (IBRITUMOMAB TIUXETAN) were performed using sequential whole body images and the MIRDOSE 3 software program. The estimated radiation absorbed doses to organs and marrow from a course of the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen are summarized in Table 1. Absorbed dose estimates for the lower large intestine, upper large intestine, and small intestine have been modified from the standard MIRDOSE 3 output to account for the assumption that activity is within the intestine wall rather than the intestine contents.

Table 1: Estimated Radiation Absorbed Doses from Y-90 Maasol (IBRITUMOMAB TIUXETAN)

None.

WARNINGS

Included as part of the PRECAUTIONS section.

PRECAUTIONS

Serious Infusion Reactions

See also prescribing information for rituximab.

Rituximab, alone or as a component of the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen, can cause severe, including fatal, infusion reactions. These reactions typically occur during the first rituximab infusion with time to onset of 30 to 120 minutes. Signs and symptoms of severe infusion reactions may include urticaria, hypotension, angioedema, hypoxia, bronchospasm, pulmonary infiltrates, acute respiratory distress syndrome, myocardial infarction, ventricular fibrillation, and cardiogenic shock. Temporarily slow or interrupt the rituximab infusion for less severe infusion reactions. Immediately discontinue rituximab and Y-90 Maasol (IBRITUMOMAB TIUXETAN) administration for severe infusion reactions. Only administer Rituxan/Maasol (IBRITUMOMAB TIUXETAN) in facilities where immediate access to resuscitative measures is available.

Prolonged And Severe Cytopenias

Cytopenias with delayed onset and prolonged duration, some complicated by hemorrhage and severe infection, are the most common severe adverse reactions of the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen. When used according to recommended doses, the incidences of severe thrombocytopenia and neutropenia are greater in patients with mild baseline thrombocytopenia ( ≥ 100,000 but ≤ 149,000/mm³) compared to those with normal pretreatment platelet counts. Severe cytopenias persisting more than 12 weeks following administration can occur. Monitor complete blood counts (CBC) and platelet counts following the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen weekly until levels recover or as clinically indicated..

Do not administer the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen to patients with ≥ 25% lymphoma marrow involvement and/or impaired bone marrow reserve. Monitor patients for cytopenias and their complications (e.g., febrile neutropenia, hemorrhage) for up to 3 months after use of the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen. Avoid using drugs which interfere with platelet function or coagulation following the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen.

Severe Cutaneous And Mucocutaneous Reactions

Erythema multiforme, Stevens-Johnson syndrome, toxic epidermal necrolysis, bullous dermatitis, and exfoliative dermatitis, some fatal, were reported in post-marketing experience. The time to onset of these reactions was variable, ranging from a few days to 4 months after administration of the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen. Discontinue the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen in patients experiencing a severe cutaneous or mucocutaneous reaction.

Altered Biodistribution

In a post-marketing registry designed to collect biodistribution images and other information in reported cases of altered biodistribution, there were 12 (1.3%) patients reported to have altered biodistribution among 953 patients registered.

Risk Of Developing Myelodysplastic Syndrome, Leukemia, And Other Malignancies

The radiation dose resulting from therapeutic exposure to Y-90 radiolabeled Maasol (IBRITUMOMAB TIUXETAN) may result in secondary malignancies.

Myelodysplastic syndrome (MDS) and/or acute myelogenous leukemia (AML) were reported in 5.2% (11/211) of patients with relapsed or refractory NHL enrolled in clinical studies and 1.5% (8/535) of patients included in the expanded-access trial, with median follow-up of 6.5 and 4.4 years, respectively. Among the 19 reported cases, the median time to the diagnosis of MDS or AML was 1.9 years following treatment with the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen; however, the cumulative incidence continues to increase.

Among 204 patients receiving Y-90 Maasol (IBRITUMOMAB TIUXETAN) following first-line chemotherapy, 26 (12.7%) patients in the Maasol (IBRITUMOMAB TIUXETAN) arm developed a second primary malignancy compared to 14 (6.8%) of patients in the control arm. Seven patients (3.4%, 7/204) were diagnosed with MDS/AML after receiving Maasol (IBRITUMOMAB TIUXETAN), compared to one patient (0.5%, 1/205) in the control arm, with a median follow-up of 7.3 years. Deaths due to second primary malignancy included 8 (3.9%) patients in the Maasol (IBRITUMOMAB TIUXETAN) arm compared to 3 (1.5%) patients in the control arm. Deaths due to MDS/AML included five (2.5%) patients in the Maasol (IBRITUMOMAB TIUXETAN) arm compared to no patients in the control arm.

Extravasation

Monitor patients closely for evidence of extravasation during Maasol (IBRITUMOMAB TIUXETAN) infusion. Immediately terminate the infusion if signs or symptoms of extravasation occur and restart in another limb.

Risks Of Immunization

The safety of immunization with live viral vaccines following the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen has not been studied. Do not administer live viral vaccines to patients who have recently received Maasol (IBRITUMOMAB TIUXETAN). The ability to generate an immune response to any vaccine following the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen has not been studied.

Radionuclide Precautions

During and after radiolabeling Maasol (IBRITUMOMAB TIUXETAN) with Y-90, minimize radiation exposure to patients and to medical personnel, consistent with institutional good radiation safety practices and patient management procedures.

Embryo-Fetal Toxicity

Based on its radioactivity, Y-90 Maasol (IBRITUMOMAB TIUXETAN) may cause fetal harm when administered to a pregnant woman. If the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen is administered during pregnancy, the patient should be apprised of the potential hazard to a fetus. Advise women of childbearing potential to use adequate contraception for a minimum of twelve months.

Nonclinical Toxicology

Carcinogenesis, Mutagenesis, Impairment Of Fertility

Carcinogenicity and mutogenicity studies have not been conducted. However, radiation is a potential carcinogen and mutagen.

No animal studies have been performed to determine the effects of Maasol (IBRITUMOMAB TIUXETAN) on fertility in males or females. In clinical studies, the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen results in a significant radiation dose to the testes: the radiation dose to the ovaries has not been established. There is a potential risk that the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen could cause toxic effects on the male and female gonads. Effective contraceptive methods should be used during treatment and for up to 12 months following the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen.

Use In Specific Populations

Pregnancy

Pregnancy Category D

Risk Summary

Based on its radioactivity, Y-90 Maasol (IBRITUMOMAB TIUXETAN) may cause fetal harm when administered to a pregnant woman.

Immunoglobulins are known to cross the placenta. There are no adequate and well-controlled studies in pregnant women. Animal reproductive toxicology studies of Maasol (IBRITUMOMAB TIUXETAN) have not been conducted.

Advise women of childbearing potential to use adequate contraception for a minimum of twelve months. Inform women who become pregnant while receiving Maasol (IBRITUMOMAB TIUXETAN) of the potential fetal risks.

Nursing Mothers

Because human IgG is excreted in human milk, it is expected that Maasol (IBRITUMOMAB TIUXETAN) would be present in human milk. Because of the potential for adverse reactions in nursing infants from Y-90 Maasol (IBRITUMOMAB TIUXETAN), a decision should be made to discontinue nursing or not administer the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen, taking into account the importance of the drug to the mother.

Pediatric Use

The safety and effectiveness of Maasol (IBRITUMOMAB TIUXETAN) have not been established in pediatric patients.

Geriatric Use

Of 349 patients with relapsed/refractory NHL treated with the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen in clinical studies, 38% (132 patients) were age 65 years and over, while 12% (41 patients) were age 75 years and over.

Of 414 patients enrolled in Study 4 (Maasol (IBRITUMOMAB TIUXETAN) following first-line chemotherapy) 206 patients received Maasol (IBRITUMOMAB TIUXETAN). Of these patients 14% (29 patients) were 65 years and over, while 2% (4 patients) were 75 years and older. In the control arm, 10% (21 patients) were 65 years or over and 0% (0 patients) were 75 years or older.

No overall differences in safety or effectiveness were observed between these subjects and younger subjects, but greater sensitivity of some older individuals cannot be ruled out.

The following serious adverse reactions are discussed in greater detail in other sections of the label:

• Serious Infusion Reactions.
• Prolonged and Severe Cytopenias.
• Severe Cutaneous and Mucocutaneous Reactions.
• Leukemia and Myelodysplastic Syndrome.

The most common adverse reactions of Maasol (IBRITUMOMAB TIUXETAN) are cytopenias, fatigue, nasopharyngitis, nausea, abdominal pain, asthenia, cough, diarrhea, and pyrexia.

The most serious adverse reactions of Maasol (IBRITUMOMAB TIUXETAN) are prolonged and severe cytopenias (thrombocytopenia, anemia, lymphopenia, neutropenia) and secondary malignancies.

Because the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen includes the use of rituximab, see prescribing information for rituximab.

Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

The reported safety data reflects exposure to Maasol (IBRITUMOMAB TIUXETAN) in 349 patients with relapsed or refractory, low-grade, follicular or transformed NHL across 5 trials (4 single arm and 1 randomized) and in 206 patients with previously untreated follicular NHL in a randomized trial (Study 4) who received any portion of the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen. The safety data reflect exposure to Maasol (IBRITUMOMAB TIUXETAN) in 270 patients with relapsed or refractory NHL with platelet counts ≥ 150,000/ mm³ who received 0.4 mCi/kg (14.8 MBq/kg) of Y-90 Maasol (IBRITUMOMAB TIUXETAN) (Group 1 in Table 4), 65 patients with relapsed or refractory NHL with platelet counts of ≥ 100,000 but ≤ 149,000/mm³ who received 0.3 mCi/kg (11.1 MBq/kg) of Y-90 Maasol (IBRITUMOMAB TIUXETAN) (Group 2 in Table 4), and 204 patients with previously untreated NHL with platelet counts ≥ 150,000/ mm³ who received 0.4 mCi/kg (14.8 MBq/kg) of Y-90 Maasol (IBRITUMOMAB TIUXETAN); all patients received a single course of Maasol (IBRITUMOMAB TIUXETAN).

Table 2 displays selected adverse reaction incidence rates in patients who received any portion of the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen (n=206) or no further therapy (n=203) following first-line chemotherapy (Study 4).

Table 2: Per-Patient Incidence (%) of Selecteda Adverse Reactions Occurring in ≥ 5% of Patients with Previously Untreated Follicular NHL Treated with the Maasol (IBRITUMOMAB TIUXETAN) Therapeutic Regimen

Table 3 shows hematologic toxicities in 349 Maasol (IBRITUMOMAB TIUXETAN)-treated patients with relapsed or refractory, low-grade, follicular or transformed B-cell NHL. Grade 2-4 hematologic toxicity occurred in 86% of Maasol (IBRITUMOMAB TIUXETAN)-treated patients.

Table 3: Per-Patient Incidence (%) of Hematologic Adverse Reactions in Patients with Relapsed or Refractory Low-grade, Follicular or Transformed B-cell NHL^a (N = 349)

Prolonged And Severe Cytopenias

Patients in clinical studies were not permitted to receive hematopoietic growth factors beginning 2 weeks prior to administration of the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen.

The incidence and duration of severe hematologic toxicity in previously treated NHL patients (N=335) and in previously untreated patients (Study 4) receiving Y-90 Maasol (IBRITUMOMAB TIUXETAN) are shown in Table 4.

Table 4: Severe Hematologic Toxicity in Patients Receiving Maasol (IBRITUMOMAB TIUXETAN)

Cytopenias were more severe and more prolonged among eleven (5%) patients who received Maasol (IBRITUMOMAB TIUXETAN) after first-line fludarabine or a fludarabine-containing chemotherapy regimen as compared to patients receiving non-fludarabinecontaining regimens. Among these eleven patients, the median platelet nadir was 13,000/mm³ with a median duration of platelets below 50,000/mm³ of 56 days and the median time for platelet recovery from nadir to Grade 1 toxicity or baseline was 35 days. The median ANC was 355/mm³, with a median duration of ANC below 1,000/mm³ of 37 days and the median time for ANC recovery from nadir to Grade 1 toxicity or baseline was 20 days.

The median time to cytopenia was similar across patients with relapsed/refractory NHL and those completing first-line chemotherapy, with median ANC nadir at 61-62 days, platelet nadir at 49-53 days, and hemoglobin nadir at 68-69 days after Y-90-Maasol (IBRITUMOMAB TIUXETAN) administration.

Information on hematopoietic growth factor use and platelet transfusions is based on 211 patients with relapsed/refractory NHL and 206 patients following first-line chemotherapy. Filgrastim was given to 13% of patients and erythropoietin to 8% with relapsed or refractory disease; 14% of patients receiving Maasol (IBRITUMOMAB TIUXETAN) following first-line chemotherapy received granulocyte-colony stimulating factors and 5% received erythopoiesis-stimulating agents. Platelet transfusions were given to approximately 22% of all Maasol (IBRITUMOMAB TIUXETAN)-treated patients. Red blood cell transfusions were given to 20% of patients with relapsed or refractory NHL and 2% of patients receiving Maasol (IBRITUMOMAB TIUXETAN) following first-line chemotherapy.

Infections

In relapsed or refractory NHL patients, infections occurred in 29% of 349 patients during the first 3 months after initiating the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen and 3% developed serious infections (urinary tract infection, febrile neutropenia, sepsis, pneumonia, cellulitis, colitis, diarrhea, osteomyelitis, and upper respiratory tract infection). Life-threatening infections were reported in 2% (sepsis, empyema, pneumonia, febrile neutropenia, fever, and biliary stent-associated cholangitis). From 3 months to 4 years after Maasol (IBRITUMOMAB TIUXETAN) treatment, 6% of patients developed infections; 2% were serious (urinary tract infection, bacterial or viral pneumonia, febrile neutropenia, perihilar infiltrate, pericarditis, and intravenous drugassociated viral hepatitis) and 1% were life-threatening infections (bacterial pneumonia, respiratory disease, and sepsis).

When administered following first-line chemotherapy (Table 2), Grade 3-4 infections occurred in 8% of Maasol (IBRITUMOMAB TIUXETAN) treated patients and in 2% of controls and included neutropenic sepsis (1%), bronchitis, catheter sepsis, diverticulitis, herpes zoster, influenza, lower respiratory tract infection, sinusitis, and upper respiratory tract infection.

Leukemia And Myelodysplastic Syndrome

Among 746 patients with relapsed/refractory NHL, 19 (2.6%) patients developed MDS/AML with a median follow-up of 4.4 years. The overall incidence of MDS/AML among the 211 patients included in the clinical studies was 5.2% (11/211), with a median follow-up of 6.5 years and median time to development of MDS/AML of 2.9 years. The cumulative Kaplan-Meier estimated incidence of MDS/secondary leukemia in this patient population was 2.2% at 2 years and 5.9% at 5 years. The incidence of MDS/AML among the 535 patients in the expanded access programs was 1.5% (8/535) with a median follow-up of 4.4 years and median time to development of MDS/AML of 1.5 years. Multiple cytogenetic abnormalities were described, most commonly involving chromosomes 5 and/or 7. The risk of MDS/AML was not associated with the number of prior treatments (0-1 versus 2-10).

Among 204 patients receiving Y-90-Maasol (IBRITUMOMAB TIUXETAN) following first-line treatment, 7 (3%) patients developed MDS/AML between approximately 2 to 7 years after Maasol (IBRITUMOMAB TIUXETAN) administration.

Post-Marketing Experience

The following adverse reactions have been identified during post-approval use of the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen in hematologic malignancies. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure. Decisions to include these reactions in labeling are typically based on one or more of the following factors: (1) seriousness of the reaction, (2) frequency of reporting, or (3) strength of causal connection to the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen.

• Cutaneous and mucocutaneous reactions: erythema multiforme, Stevens-Johnson syndrome, toxic epidermal necrolysis, bullous dermatitis, and exfoliative dermatitis.
• Infusion site erythema and ulceration following extravasation.
• Radiation injury in tissues near areas of lymphomatous involvement within a month of Maasol (IBRITUMOMAB TIUXETAN) administration.

Immunogenicity

As with all therapeutic proteins, there is a potential for immunogenicity. The incidence of antibody formation is highly dependent on the sensitivity and specificity of the assay. Additionally, the observed incidence of antibody (including neutralizing antibody) positivity in an assay may be influenced by several factors including assay methodology, sample handling, timing of sample collection, concomitant medications, and underlying disease. For these reasons, comparisons of the incidence of HAMA/HACA to the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen with the incidence of antibodies to other products may be misleading.

HAMA and HACA response data on 446 patients from 8 clinical studies conducted over a 10-year time period are available. Overall, 11/446 (2.5%) had evidence of either HAMA formation (N=8) or HACA formation (N=4). Six of these patients developed HAMA/HACA after treatment with Maasol (IBRITUMOMAB TIUXETAN) and 5 were HAMA/HACA positive at baseline. Of the 6 who were HAMA/HACA positive, only one was positive for both. Furthermore, in 6 of the 11 patients, the HAMA/HACA reverted to negative within 2 weeks to 3 months. No patients had increasing levels of HAMA/HACA at the end of the studies.

Only 6/446 patients (1.3%) had developed evidence of antibody formation after treatment with Maasol (IBRITUMOMAB TIUXETAN), and of these, many either reverted to negative or decreased over time. This data demonstrates that HAMA/HACA develop infrequently, are typically transient, and do not increase with time.

Severe cytopenias which may require stem cell support have occurred at doses higher than the recommended maximum total dose of 32 mCi (1184 MBq).

In clinical studies, administration of the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen resulted in sustained depletion of circulating B cells. At four weeks, the median number of circulating B cells was zero (range, 0-1084/mm³). B-cell recovery began at approximately 12 weeks following treatment, and the median level of B cells was within the normal range (32 to 341/mm³) by 9 months after treatment. Median serum levels of IgG and IgA remained within the normal range throughout the period of B-cell depletion. Median IgM serum levels dropped below normal (median 49 mg/dL, range 13- 3990 mg/dL) after treatment and recovered to normal values by 6-months post therapy.

Pharmacokinetic and biodistribution studies were performed using In-111 Maasol (IBRITUMOMAB TIUXETAN) (5 mCi [185 MBq] In-111, 1.6 mg ibritumomab tiuxetan). In an early study designed to assess the need for pre-administration of unlabeled antibody, only 18% of known sites of disease were imaged when In-111 Maasol (IBRITUMOMAB TIUXETAN) was administered without unlabeled ibritumomab. When preceded by unlabeled ibritumomab (1.0 mg/kg or 2.5 mg/kg), In-111 Maasol (IBRITUMOMAB TIUXETAN) detected 56% and 92% of known disease sites, respectively. These studies were conducted with a Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen that included unlabeled ibritumomab.

In pharmacokinetic studies of patients receiving the Maasol (IBRITUMOMAB TIUXETAN) therapeutic regimen, the mean effective half-life for Y-90 activity in blood was 30 hours, and the mean area under the fraction of injected activity (FIA) vs. time curve in blood was 39 hours. Over 7 days, a median of 7.2% of the injected activity was excreted in urine.