Fasenra is given every 4 weeks for the first 3 doses, then every 8 weeks after that for as long as treatment continues. The 30 mg injection is the same dose every time, with no weight-based adjustments. This two-phase schedule, a short loading period followed by less frequent maintenance injections, is one of the least demanding dosing schedules among asthma biologics.
The Two-Phase Dosing Schedule
The first three injections are spaced 4 weeks apart. This loading phase builds up enough of the drug in your system to start depleting eosinophils, the white blood cells that drive inflammation in severe eosinophilic asthma. After those initial three doses, you switch to one injection every 8 weeks for as long as you and your doctor decide to continue treatment.
That means in the first year, you’ll receive roughly 8 injections total: 3 during the loading phase (at weeks 0, 4, and 8) and then approximately 5 more at 8-week intervals. In subsequent years, you’ll need around 6 or 7 injections per year depending on scheduling.
Why Every 8 Weeks Works
Fasenra (benralizumab) has a half-life of about 15 days, meaning it takes that long for half the drug to clear your body. But the clinical effect lasts much longer than the drug itself. In studies, eosinophil counts stayed at or near zero for at least 8 weeks after the last dose, which is why the longer maintenance interval holds up. The three loading doses bring eosinophil levels down quickly, and by the time you’re on the 8-week schedule, the suppression is sustained at steady state.
FDA reviewers confirmed there was no meaningful difference in eosinophil control between patients dosed every 4 weeks and those dosed every 8 weeks after the loading phase. The longer interval works just as well, with fewer trips to the clinic.
How Well the 8-Week Schedule Performs
The SIROCCO trial, a large phase 3 study published in The Lancet, tested the every-8-week maintenance schedule in patients with severe asthma uncontrolled by high-dose inhalers. Over 48 weeks, patients on the 8-week regimen had 51% fewer asthma exacerbations compared to placebo. Lung function also improved: the group saw an average increase of 0.159 liters in a standard breathing test (FEV1), a clinically meaningful gain for people with severe disease.
Long-term data from the BORA extension trial, which followed patients through a second year of treatment, showed these benefits held steady. There were no new safety concerns from prolonged eosinophil depletion, and the rate of adverse events, including infections, was similar between patients on Fasenra and those who had originally been on placebo. The dosing schedule stays the same in year two and beyond, with no need for adjustments.
How Fasenra Compares to Other Biologics
The 8-week maintenance interval is the longest among commonly prescribed asthma biologics. Mepolizumab (Nucala) requires an injection every 4 weeks. Dupilumab (Dupixent) is injected every 2 weeks. For patients who want fewer injections, Fasenra’s schedule is a practical advantage, cutting the number of doses roughly in half compared to monthly alternatives.
Getting Your Injection
Each dose is a single 30 mg subcutaneous injection. Fasenra is available as a prefilled syringe and as an autoinjector pen. Your first few doses will typically be given in a healthcare setting so your provider can monitor for any allergic reactions. Once you and your doctor are comfortable, self-injection at home is an option with the autoinjector, which can make the 8-week schedule even more convenient since you won’t need a clinic visit every time.
The injection is given in the upper arm, thigh, or abdomen. It takes only a few seconds to administer. Most patients don’t need to set aside significant time for the process itself.
What to Do if You Miss a Dose
If you miss a scheduled injection, contact your healthcare provider to reschedule as soon as possible. Because the drug’s eosinophil-suppressing effect lasts at least 8 weeks, a short delay is unlikely to cause an immediate loss of control, but getting back on schedule matters for maintaining consistent protection against flare-ups. Your provider will advise on timing your next dose and whether to adjust the schedule going forward.