Background Cetuximab (CTX) (Erbitux) is a chimeric mouse-human monoclonal antibody IgG1 targeting epidermal growth factor receptor (EGFR). It is approved for use as treatment for metastatic colorectal cancer and squamous cell carcinoma of the head and neck.

Purpose To evaluate the biological activity (BA) that remains in Erbitux after opening single-use vials in a long-term study. It was also to evaluate the remaining activity when the opened medicine was exposed to different stress conditions to test the risk associated with accidental exposure to light, heat, etc.

Material and methods An indirect non-competitive ELISA was developed for the purpose based in the use of human EGFR to test the BA of CTX. Calibration function was between 0.4–50.0 µg/mL, detection and quantification limits were 0.1 and 0.4 µg/mL; precision - as intraday and interday reproducibility (%RSD) - was <10% and accuracy (% of recovery) >90%. Cross-reaction with similar antibodies was tested. Surplus samples of Erbitux from the daily use of the Hospital Pharmacy Unit were stored at 4°C and −20°C protected from light. BA was tested up to 30 days. A drug degradation study (mild experimental conditions) was also conducted.

Results The BA of Erbitux decreased 5% when stored for 24 h at 4°C. The decrease was 14% after 3 days, 20% after 7 days and 85% on the last day checked. For CTX samples stored frozen at -20°C, the BA decreased from 16% (24 h) to 85% on the last day checked. Residual BA remained in all samples submitted to the stress except in samples heated at 70°C. There were no cross reactions.

Conclusion Regarding the BA of Erbitux, it is stable within the 24 first hours after opening of the vial when stored at 4°C. These results will be further investigated by flow cytometry.

References and/or acknowledgements Financial support: PI10/00201 (MICINN, Government of Spain).

No conflict of interest.