Three different procedures have been used for detecting antibodies to Roferon-A (recombinant human interferon alfa-2a, rHuIFN alpha-2a) in the serum of patients who received this interferon as part ...of ongoing clinical trials: an antiviral neutralization bioassay (ANB), the standard method recommended by the World Health Organization (WHO), and the more recently developed radioimmunoassay (RIA) and enzymeimmunoassay (EIA). Although the three tests are based on different principles, the correlation among them was excellent. The assays show differences in sensitivities with the ANB being the least sensitive of the three. The EIA equals the RIA in sensitivity, reproducibility, accuracy and labor and provides the advantage of safety and convenience in the use of non-radioactive materials. Therefore, the EIA has been selected as the most suitable assay for initial screening of the sera of patients receiving Roferon-A for the presence of antibodies to this interferon. EIA positive sera are then tested in the ANB to determine whether or not neutralizing activities are present.
Eighteen patients with advanced solid cancer were treated with daily 5'-dFUrd infusions given over 1 h on days 1-5 of a 4-week cycle. Nine patients received 3 g/m2 5'-dFUrd daily and another nine ...patients 5 g/m2. One patient on 5 g/m2 5'-dFUrd was not fully evaluable for tolerability due to early death (progressive disease) 4 weeks after the first cycle. A total of 48 cycles was given. The gastrointestinal and hematological toxicity was generally mild (grade 1-2). Central neurotoxicity (ataxia, unsteadiness, diplopia, dysarthria, sometimes confusion) was observed in 7 of 8 patients on 5 g/m2 5'-dFUrd leading to premature discontinuation of treatment in 3 patients (after 2 cycles). Only 3 of the 9 patients in the 3 g/m2 group had slight signs of cerebellopathy. Typically, the reversible neurological side effects started at the end of the 2nd week of a cycle. The serum elimination kinetics of 5'-dFUrd and its metabolites 5-FU and 5'-dFUH2 have been investigated in the serum and showed very low intra- and interindividual variations. Peak concentrations of the 5'-dFUrd at the end of the infusion approximated 500 mumol/l and 1000 mumol/l for the 3 g/m2 and 5 g/m2 group, respectively. The peak of the serum 5-FU was reached at the same time, the ratio 5-FU/5'-dFUrd being around 10%. The elimination half-life time for 5-FU was protracted by a factor of 2-3 compared with the direct injection of 5-FU. Monthly infusion of 5'-dFUrd 5 mg/m2 per day on days 1-5 lead to an unacceptable frequency and degree of neurological toxicity. Similar infusions of 5'-dFUrd 3 g/m2 per day on days 1-5 were well tolerated.
