TYSABRI (Page 4 of 7)

6.2 Immunogenicity

As with all therapeutic proteins, there is a potential for immunogenicity. The detection 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, comparison of the incidence of antibodies to natalizumab in the studies described below with the incidence of antibodies in other studies or to other products may be misleading.

Patients in Study MS1 [see Clinical Studies (14.1) ] were tested for antibodies to natalizumab every 12 weeks. The assays used were unable to detect low to moderate levels of antibodies to natalizumab. Approximately 9% of patients receiving TYSABRI developed detectable antibodies at least once during treatment. Approximately 6% of patients had positive antibodies on more than one occasion. Approximately 82% of patients who became persistently antibody-positive developed detectable antibodies by 12 weeks. Anti-natalizumab antibodies were neutralizing in vitro.

The presence of anti-natalizumab antibodies was correlated with a reduction in serum natalizumab levels. In Study MS1, the Week 12 pre-infusion mean natalizumab serum concentration in antibody-negative patients was 15 mcg/mL compared to 1.3 mcg/mL in antibody-positive patients. Persistent antibody-positivity resulted in a substantial decrease in the effectiveness of TYSABRI. The risk of increased disability and the annualized relapse rate were similar in persistently antibody-positive TYSABRI-treated patients and patients who received placebo. A similar phenomenon was also observed in Study MS2.

Infusion-related reactions that were most often associated with persistent antibody-positivity included urticaria, rigors, nausea, vomiting, headache, flushing, dizziness, pruritus, tremor, feeling cold, and pyrexia. Additional adverse reactions more common in persistently antibody-positive patients included myalgia, hypertension, dyspnea, anxiety, and tachycardia.

Patients in CD studies [see Clinical Studies (14.2) ] were first tested for antibodies at Week 12, and in a substantial proportion of patients, this was the only test performed given the 12-week duration of placebo-controlled studies. Approximately 10% of patients were found to have anti-natalizumab antibodies on at least one occasion. Five percent (5%) of patients had positive antibodies on more than one occasion. Persistent antibodies resulted in reduced efficacy and an increase in infusion-related reactions with symptoms that include urticaria, pruritus, nausea, flushing, and dyspnea.

The long-term immunogenicity of TYSABRI and the effects of low to moderate levels of antibody to natalizumab are unknown [see Warnings and Precautions (5.5), Adverse Reactions (6.1)].

6.3 Postmarketing Experience

The following adverse reactions have been identified during post approval use of TYSABRI. 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.

Blood disorders: hemolytic anemia, thrombocytopenia (including immune thrombocytopenic purpura).


Because of the potential for increased risk of PML and other infections, Crohn’s disease patients receiving TYSABRI should not be treated with concomitant immunosuppressants (e.g., 6-mercaptopurine, azathioprine, cyclosporine, or methotrexate) or inhibitors of TNF-α, and corticosteroids should be tapered in those patients with Crohn’s disease who are on chronic corticosteroids when they start TYSABRI therapy [see Indications and Usage (1.2), Warnings and Precautions (5.1, 5.6)]. Ordinarily, MS patients receiving chronic immunosuppressant or immunomodulatory therapy should not be treated with TYSABRI [see Indications and Usage (1.1), Warnings and Precautions (5.1, 5.6)].


8.1 Pregnancy

Risk Summary

There are no adequate data on the developmental risk associated with the use of TYSABRI in pregnant women. In animal studies, administration of natalizumab during pregnancy produced fetal immunologic and hematologic effects in monkeys at doses similar to the human dose and reduced offspring survival in guinea pigs at doses greater than the human dose. These doses were not maternally toxic but produced the expected pharmacological effects in maternal animals [see Data ].

In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2-4% and 15-20%, respectively. The background risk of major birth defects and miscarriage for the indicated population is unknown.


Animal Data

In developmental toxicity studies conducted in guinea pigs and monkeys, at natalizumab doses up to 30 mg/kg (7 times the recommended human dose based on body weight [mg/kg]), transplacental transfer and in utero exposure of the embryo/fetus was demonstrated in both species.

In a study in which pregnant guinea pigs were administered natalizumab (0, 3, 10, or 30 mg/kg) by intravenous (IV) infusion on alternate days throughout organogenesis (gestation days [GD] 4-30), no effects on embryofetal development were observed.

When pregnant monkeys were administered natalizumab (0, 3, 10, or 30 mg/kg) by IV infusion on alternative days throughout organogenesis (GDs 20-70), serum levels in fetuses at delivery were approximately 35% of maternal serum natalizumab levels. There were no effects on embryofetal development; however, natalizumab-related immunological and hematologic changes were observed in the fetuses at the two highest doses. These changes included decreases in lymphocytes (CD3+ and CD20+), changes in lymphocyte subpopulation percentages, mild anemia, reduced platelet count, increased spleen weights, and reduced liver and thymus weights associated with increased splenic extramedullary hematopoiesis, thymic atrophy, and decreased hepatic hematopoiesis.

In a study in which monkeys were exposed to natalizumab during pregnancy (IV infusion of 30 mg/kg) on alternate days from GD20 to GD70 or GD20 to term, abortions were increased approximately 2-fold compared to controls. In offspring born to mothers administered natalizumab on alternate days from GD20 until delivery, hematologic effects (decreased lymphocyte and platelet counts) were also observed. These effects were reversed upon clearance of natalizumab. There was no evidence of anemia in these offspring. Offspring exposed in utero and during lactation had a normal immune response to challenge with a T-cell dependent antigen.

In a study in which pregnant guinea pigs were exposed to natalizumab (30 mg/kg IV) on alternate dates during GDs 30-64, a reduction in pup survival was observed.

8.2 Lactation

Risk Summary

Natalizumab has been detected in human milk. There are no data on the effects of this exposure on the breastfed infant or the effects of the drug on milk production.

The developmental and health benefits of breastfeeding should be considered along with the mother’s clinical need for TYSABRI and any potential adverse effects on the breastfed infant from TYSABRI or from the underlying maternal condition.

8.4 Pediatric Use

Safety and effectiveness in pediatric patients with multiple sclerosis or Crohn’s disease below the age of 18 years have not been established. TYSABRI is not indicated for use in pediatric patients.

8.5 Geriatric Use

Clinical studies of TYSABRI did not include sufficient numbers of patients aged 65 years and over to determine whether they respond differently than younger patients. Other reported clinical experience has not identified differences in responses between the elderly and younger patients.


Safety of doses higher than 300 mg has not been adequately evaluated. The maximum amount of TYSABRI that can be safely administered has not been determined.


Natalizumab is a recombinant humanized IgG4κ monoclonal antibody produced in murine myeloma cells. Natalizumab contains human framework regions and the complementarity-determining regions of a murine antibody that binds to α4-integrin. The molecular weight of natalizumab is 149 kilodaltons.

TYSABRI (natalizumab) injection is supplied as a sterile, colorless, and clear to slightly opalescent solution for intravenous infusion. Each 15 mL of solution contains 300 mg natalizumab; sodium chloride, USP (123 mg); sodium phosphate, monobasic, monohydrate, USP (17 mg); sodium phosphate, dibasic, heptahydrate, USP (7.24 mg); polysorbate 80, USP/NF (3 mg), in Water for Injection, USP at pH 6.1.

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