ADVERSE REACTIONS
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 adverse reaction information from clinical trials does, however, provide a basis for identifying the adverse events that appear to be related to drug use and for approximating rates.
The data described below reflect exposure to ELITEK in 703 patients [63% male, 37% female; median age 10 years (range 10 days to 88 years); 73% Caucasian, 9% African, 4% Asian, 14% other/unknown]. ELITEK was studied for adverse reactions, regardless of severity, in 347 patients (265 pediatric and 82 adults) enrolled in one active-controlled trial (Study 1), two uncontrolled trials (Studies 2 and 3), and one uncontrolled safety trial (n=82). Additionally, an expanded access experience enrolled 356 patients, for whom reliably collected data were limited to serious adverse reactions.
Among the 703 patients for whom serious adverse reactions were assessed, the most serious adverse reactions caused by ELITEK were allergic reactions including anaphylaxis (<1%), rash (1%), hemolysis (<1%), and methemoglobinemia (<1%) (see BOX WARNINGS and WARNINGS). The commonly observed serious adverse reactions were fever (5%), neutropenia with fever (4%), respiratory distress (3%), sepsis (3%), neutropenia (2%), and mucositis (2%). The following additional serious adverse reactions were observed in </=1% of patients regardless of causality: acute renal failure, arrhythmia, cardiac failure, cardiac arrest, cellulitis, cerebrovascular disorder, chest pain, convulsions, cyanosis, diarrhea, dehydration, hot flushes, ileus, infection, intestinal obstruction, hemorrhage, myocardial infarction, paresthesia, pancytopenia, pneumonia, pulmonary edema, pulmonary hypertension, retinal hemorrhage, rigors, thrombosis, and thrombophlebitis.
Among the 347 patients for whom all adverse reactions regardless of severity were assessed, the most frequently observed adverse reactions (incidence >/=10%) were vomiting (50%), fever (46%), nausea (27%), headache (26%), abdominal pain (20%), constipation (20%), diarrhea (20%), mucositis (15%), and rash (13%). In Study 1, an active control study, the following adverse events occurred more frequently in ELITEK-treated subjects than allopurinol-treated subjects: vomiting, fever, nausea, diarrhea, and headache. Although the incidence of rash was similar in the two arms, severe rash (NCI CTC3, Grade 3 or 4) was reported only in one ELITEK-treated patient.
IMMUNOGENICITY
ELITEK is immunogenic in healthy volunteers, and can elicit antibodies that inhibit the activity of rasburicase in vitro (see BOX WARNINGS, Anaphylaxis and WARNINGS, Anaphylaxis).
In a study of 28 healthy volunteers, the incidence of antibody responses to either a single dose or to 5 daily doses was assessed. Binding antibodies to rasburicase were detected by ELISA in 17/28 (61%) volunteers and neutralizing antibodies were detected in 18/28 (64%) volunteers. Time to detection of antibodies ranged from 1 to 6 weeks after ELITEK exposure. In two subjects with extended follow-up, antibodies persisted for 333 and 494 days.
The incidence of antibody responses in patients with hematologic malignancy has not been adequately assessed. In clinical trials of patients with hematologic malignancies, 24 of the 218 patients tested (11%) developed antibodies by day 28 following ELITEK administration. However, this is not a reliable estimate of the true incidence of antibody responses in patients with hematologic malignancies, because the data from the healthy volunteer study indicate that antibody may not be detectable until some time point beyond day 28.
The incidence of antibody responses detected is highly dependent on the sensitivity and specificity of the assay, which have not been fully evaluated. Additionally, the observed incidence of antibody positivity in an assay may be influenced by several factors, including serum sampling, timing and methodology, concomitant medications, and underlying disease. For these reasons, comparison of the incidence of antibodies to ELITEK with the incidence of antibodies to other products may be misleading.
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