Appendix A.

Formulas for Cost-effectiveness calculations of FeNO + Omalizumab vs Omalizumab Only

Strategy to identify responders	Expected per-patient costs (trial period only)	Expected rate of responders identified	Expected cost per responder (trial period only)	Expected per-patient costs (trial + initial Tx period)
FeNO Measurement + omalizumab Trial	$d+0.51\left(abc\right)$	0.51	$\frac{\mathrm{T}\mathrm{r}\mathrm{i}\mathrm{a}\mathrm{l}\mathrm{P}\mathrm{e}\mathrm{r}\mathrm{i}\mathrm{o}\mathrm{d}\mathrm{C}\mathrm{o}\mathrm{s}\mathrm{t}\mathrm{s}}{0.51}$	$(0.51abe)+\mathrm{T}\mathrm{r}\mathrm{i}\mathrm{a}\mathrm{l}\mathrm{p}\mathrm{e}\mathrm{r}\mathrm{i}\mathrm{o}\mathrm{d}\mathrm{c}\mathrm{o}\mathrm{s}\mathrm{t}\mathrm{s}$
Omalizumab trial only	$\left(abc\right)$	0.55	$\frac{\mathrm{T}\mathrm{r}\mathrm{i}\mathrm{a}\mathrm{l}\mathrm{P}\mathrm{e}\mathrm{r}\mathrm{i}\mathrm{o}\mathrm{d}\mathrm{C}\mathrm{o}\mathrm{s}\mathrm{t}\mathrm{s}}{0.55}$	$(0.55abe)+\mathrm{T}\mathrm{r}\mathrm{i}\mathrm{a}\mathrm{l}\mathrm{p}\mathrm{e}\mathrm{r}\mathrm{i}\mathrm{o}\mathrm{d}\mathrm{c}\mathrm{o}\mathrm{s}\mathrm{t}\mathrm{s}$

Notes: FeNO measurement + omalizumab trials include pathways 1 and 2. Omalizumab trial only includes pathways 3–5. Patients do not continue treatments on pathways 2, 4, or 5, so no treatment costs are incurred for those pathways.

a, payor costs of 1 vial of 150 mg of omalizumab ($713.70); b, number of vials per month (2); c, number of months in omalizumab trials (3); d, payer cost of FeNO measurements to predict ICS response ($23.20); e, number of months of omalizumab prescription following successful omalizumab trial (12).

Abbreviation: FeNO, fractional exhaled nitric oxide.