Based on these two findings, nonresponse to omalizumab within the first 12 weeks of treatment may be best assessed by applying the “2 x 4 rule”:
- When baseline IgE levels fail to double within the first 4 weeks of treatment, nonresponse needs to be expected. The “2 x 4 rule” may be especially helpful in patients with low IgE.
- One of three patients with low IgE, in our study, failed to respond to omalizumab by week 12 of treatment.