Our inaugural monoclonal antibody (Mab) of the week is omalizumab (Xolair). Before even getting into this, the package insert for Xolair has my favorite side effect of all time: feeling of impending doom. Anxious? Feeling nervous? Like the world is crashing down on you? Well, have you considered the possibility of Xolair tainting your water supply?

Jokes aside, Xolair is a great medication for allergic asthma, and is usually last-line in asthma step therapy after high-dose inhaled corticosteroids + long-acting beta agonists + long-acting muscarinic antagonist +as needed shorting-acting beta agonist (that’s a lot of inhaling). Notably, to be prescribed Xolair, you must be 6 years or older. Patients must also have an elevated IgE level, such that Xolair may provide a benefit in reducing its level.

On that note, mechanistically Xolair works by inhibiting the binding of IgE to high-affinity IgE receptors on the body’s mast cells and basophils, reducing the release of mediators in the allergic response. This leads to a reduction in IgE levels over time, and has been shown to reduce asthma exacerbations in patients with allergic asthma.
Patients on Xolair can expect to start seeing results within 6-12 weeks of starting therapy and has a half-life of ~25 days. With those being the pharmacokinetic properties, Xolair is usually dosed every 2-4 weeks as a SubQ injection, HOWEVER, just because it is a SubQ injection does not mean it can be taken at home. No, these patients have to make the long drive to some form of infusion center so they can be watched post-injection, as Xolair has a BLACK BOX WARNING for anaphylactic reactions, even after up to 1 year of receiving therapy. Therefore, patients are monitored following injection (2 hours after for the first 3 injections then 30 minutes every one thereafter).

The most common side effects to be aware of are injection site reaction (who saw that coming?), headache (as always), and anaphylaxis. There are other side effects, but their incidence isn’t notable enough for me to even include them here. Additionally, therapy with Xolair can be considered in pregnancy when other step-therapy has proven ineffective, and the same can be said for breastfeeding.

Xolair interacts with exactly two things at the time of writing, and they are so rare that I only feel obligated to include them for completion’s sake. The two agents are: *checks notes* efgartigimod alfa and loxapine. If you are on either of those agents, Xolair probably isn’t for you.

Well, that wraps up our inaugural mab of the week. I hope you’ve found this to be informative and somewhat fun to read. Stay tuned for more mabs and mab accessories in the next writing of mab of the week.
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