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warnings and cautions
5 WARNINGS AND PRECAUTIONS Serious Hypersensitivity Reactions: Serious hypersensitivity reactions occurred. ( 5.1 ) Monitoring Methotrexate Concentration: Measure methotrexate concentrations within 48 hours following VORAXAZE administration using a chromatographic method; immunoassays are unreliable for samples collected within 48 hours following VORAXAZE administration. ( 5.2 ) 5.1 Serious Hypersensitivity Reactions Serious hypersensitivity reactions occurred in less than 1% of patients [ see Adverse Reactions ( 6.1 ) ]. 5.2 Interference with Immunoassay Measurements of Methotrexate DAMPA (4-deoxy-4-amino-N 10 - methylpteroic acid), an inactive metabolite of methotrexate formed following VORAXAZE administration, interferes with the measurement of methotrexate concentration using immunoassays. This interference results in an overestimation of the methotrexate concentration. Based on the half-life of DAMPA (about 9 hours), VORAXAZE may interfere with the measurement of methotrexate concentration for up to 48 hours following a VORAXAZE dose [see Clinical Pharmacology ( 12.1 ) ]. When measuring methotrexate concentration following a VORAXAZE dose, a chromatographic method is preferred over an immunoassay.
6 ADVERSE REACTIONS The following clinically significant adverse reactions are described elsewhere in the labeling: Serious Hypersensitivity Reactions [Warnings and Precautions ( 5.1 )]. The most common related adverse events (>1%) were paresthesia, flushing, nausea and/or vomiting, hypotension and headache. ( 6 ) To report SUSPECTED ADVERSE REACTIONS, contact BTG at 877-377-3784 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch . 6.1 Clinical Trials Experience Because clinical trials are conducted under controlled but widely varying conditions, adverse reaction rates observed in clinical trials of VORAXAZE cannot be directly compared to rates in the clinical trials of other drugs and may not reflect the rates observed in practice. The evaluation of adverse reactions in patients who received VORAXAZE was confounded, because patients had toxic plasma methotrexate concentration due to prolonged methotrexate clearance, which is associated with myelosuppression, mucositis, acute hepatitis, and renal dysfunction and failure. The safety of VORAXAZE is based on data from 290 patients who were enrolled in Study 1 or Study 2, two single-arm, open-label, multicenter studies conducted in patients who had markedly delayed methotrexate clearance due to impaired renal function. Patients with osteosarcoma were eligible for these studies if the plasma methotrexate concentration was >50 µmol/L at 24 hours, >5 µmol/L at 48 hours, or >2 standard deviations above the mean methotrexate elimination curve at least 12 hours after methotrexate administration; and there was a ≥2-fold increase in serum creatinine above baseline. All other patients were eligible for these studies if the plasma methotrexate concentration was >10 µmol/L more than 42 hours after the start of the methotrexate or the plasma methotrexate concentration was >2 standard deviations above the mean methotrexate excretion curve at least 12 hours following methotrexate; and the serum creatinine was >1.5 times the upper limit of normal (ULN) or the creatinine clearance (CLcr) was <60 mL/min at least 12 hours following methotrexate administration. Safety data was available for 149 patients enrolled in Study 1. The protocol specified that patients with pre-VORAXAZE methotrexate concentration >100 μmol/L were to receive a second VORAXAZE dose 48 hours after the first dose; that patients continue receiving intravenous hydration, urinary alkalinization and leucovorin; and that leucovorin administration be adjusted to ensure that it was not administered within 2 hours before or after a VORAXAZE dose. VORAXAZE-related adverse reactions were collected on a flow sheet with a daily log of adverse reactions characterized as “glucarpidase toxicity”. Additional safety information was collected from clinical records submitted by treating physicians. This safety information was abstracted and categorized using the National Cancer Institute (NCI) Common Terminology Criteria for Adverse Events (CTCAE) version 3. One (n=106) or 2 (n= 30) doses of VORAXAZE were administered; the number of doses was not specified for 13 patients. Doses ranged from 18 Units/kg to 98 Units/kg, with a median dose of 49 Units/kg. The median age was 18 years (1 month to 85 years); 63% were male; and the underlying malignancies were osteosarcoma/sarcomas in 32% and leukemia or lymphoma in 63% of patients. Safety data was available for 141 patients enrolled in Study 2. The protocol did not specify the criterion for allowing patients to receive a second VORAXAZE dose. The protocol specified that patients continue receiving intravenous hydration, urinary alkalinization and leucovorin and that leucovorin administration be adjusted to ensure that it was not administered within 2 hours before or after VORAXAZE. VORAXAZE-related adverse reactions were collected and severity was graded according to NCI CTCAE version 3. One (n=122) or 2 (n= 18) doses of VORAXAZE were administered; the number of doses was not specified for 1 patient. Doses ranged from 6 Units/kg to 189 Units/kg, with a median dose of 50 Units/kg. The median age was 17 years (6 months to 85 years); 64% were male; and the underlying malignancies were osteogenic sarcoma in 32% and leukemia or lymphoma in 62% of patients. Among the 290 patients, 8 deaths occurred within 30 days of VORAXAZE exposure that were not related to progressive disease. The most common adverse reactions (reported in >1%) were paresthesia, flushing, and nausea and/or vomiting. Table 1 summarizes select adverse reactions; adverse reactions likely associated with toxic methotrexate plasma concentrations, such as hematological, renal and hepatic adverse reactions, were not included in this table. Table 1: Select Adverse Reactions Occurring in Patients Receiving VORAXAZE in Study 1 and Study 2 1 This incidence includes the following terms: flushing, feeling hot, burning sensation. 2 One of these reactions was classified as Grade 3. Adverse Reaction VORAXAZE N= 290 Grades 1 and 2 2 (%) Paresthesia 2 Flushing 1,2 2 Nausea/Vomiting 2 Headache 1 Hypotension 1 Blurred Vision <1 Diarrhea <1 Hypersensitivity <1 Hypertension <1 Rash <1 Throat irritation/Throat tightness <1 Tremor <1 6.2 Immunogenicity As with all therapeutic proteins, there is 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 incidence of antibodies in the studies described below with the incidence of antibodies in other studies or to other glucarpidase products may be misleading. In clinical trials, 121 patients who received one (n=99), 2 (n=21), or 3 (n=1) doses of VORAXAZE were evaluated for anti-glucarpidase antibodies. Twenty-five of these 121 patients (21%) had detectable anti-glucarpidase antibodies following VORAXAZE administration, of which 19 received 1 dose of VORAXAZE and 6 received 2 doses of VORAXAZE. Antibody titers were determined using a bridging enzyme-linked immunosorbent assay (ELISA) for anti- glucarpidase antibodies. Neutralizing antibodies were detected in 11 of the 25 patients who tested positive for anti- glucarpidase binding antibodies. Eight of these 11 patients had received a single dose of VORAXAZE; however, the development of neutralizing antibodies may be underreported due to lack of assay sensitivity.