Cautions

As with other biologics, the optimal certolizumab concentration depends upon patient-specific factors including co-morbidities, disease, and desired therapeutic endpoint.

Trough blood collection (just before the next dose) is suitable because target ranges and therapeutic cut-offs are established by clinical studies that typically evaluate trough concentrations.

Therefore, the timing of specimen collection should be considered when interpreting drug concentrations. Drug half-life should be factored in when evaluating non-trough concentrations.

Adequate drug trough levels do not guarantee clinical efficacy since primary non-response can be due to mechanistic failure.

Lack of clinical response may be due to inadequate drug exposure, immunogenicity or mechanistic mismatch. Positive anti-certolizumab antibodies should be interpreted in the context of the concomitant free certolizumab drug level.