Background The appropriate dose and frequency of omalizumab in patients with severe asthma was determined in clinical trials based on body weight (kg) and baseline IgE (IU/mL). However, in clinical practice a conversion chart promoted by stakeholders is used for dose determination.

Purpose To assess the correlation between omalizumab´s estimated dose calculated from the formula used in pivotal clinical trials (PCT) and prescribed omalizumab dose in clinical practice. We also aimed to analyse the effectiveness of omalizumab based on FEV modifications from baseline.

Material and methods Asthmatic patients treated with omalizumab up to July 2015 were evaluated retrospectively. Demographic data (gender and age), body weight, posology (dose and frequency), duration of treatment, baseline and current IgE level, and baseline and current FEV were recorded. Omalizumab estimated dose was calculated according to the PVT formula at baseline: 0.016*weight*IgE (UI/mL) every 4 weeks or 0.008*weight*IgE (UI/mL) every 2 weeks. For patients treated with omalizumab for 3 or more years current weight and IgE was used instead of baseline data to assess omalizumab´s estimated dose. Also, to analyse the effectiveness of treatment, we calculated the difference in FEV from baseline. Statistical analysis were performed using SPSS15.

Results 60 patients met the inclusion criteria. 68.3% were female and mean age was 51.8 years (range 16–80). Mean FEV improvement from baseline was 9.69% (range -25%-51.1%). This meant that 56.9% of patients developed an improvement in FEV but 25% had worsening FEV and in 18.3% of patients these data were missing. Comparison between the prescribed dose and estimated dose from the PCT formula showed a concordance of doses in only 20% of cases. Based on these data, 46.3% of patients would benefit from omalizumab dose reduction. Also, 36.7% of patients had a lower prescribed dose than omalizumab’s estimated dose based on the PCT formula. Nevertheless, 61.1% of these patients would not need an increase in dose based on FEV improvement from baseline.

Conclusion We found a great discrepancy between estimated omalizumab dose by the PCT formula and the prescribed omalizumab dose in clinical practice. By using the formula we optimised the efficiency of treatment with omalizumab.

No conflict of interest.