Gefurulimab
An investigational treatment for Myasthenia Gravis.
Drug facts
The same compound appears under different names depending on the context. Here is how to identify Gefurulimab wherever you encounter it, plus the key facts at a glance.
- Generic name
- Gefurulimab
- Development code
- ALXN1720
- Drug class
- Complement C5 inhibitor (bispecific nanobody)
- Manufacturer
- Alexion, AstraZeneca Rare Disease
- How it's taken
- Injection under the skin once a week, under FDA review
An investigational once-weekly injection under the skin for adults with generalized myasthenia gravis who test positive for antibodies against the acetylcholine receptor (AChR)[6].
- AstraZeneca says its US application is under review, and no FDA decision date has been made public[1].
- AstraZeneca says gefurulimab is approved in Japan and other countries, and on September 17, 2026 the European Medicines Agency's committee (CHMP) recommended EU approval under the brand name Klygefa[1][2].
- In the Phase 3 PREVAIL trial, gefurulimab improved scores on the MG-ADL daily-living scale by 1.6 points more than placebo at week 26[6].
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Where Gefurulimab fits
Gefurulimab is an investigational C5 complement blocker under FDA review for adults with AChR antibody-positive generalized myasthenia gravis, given as a once-weekly self-injection under the skin[1].
- The FDA has already approved 3 C5 blockers for the same group: Soliris, an IV infusion every 2 weeks after loading doses, Ultomiris, an IV infusion every 8 weeks in adults after a loading dose, and Zilbrysq, a daily injection under the skin, and each carries a boxed warning for serious meningococcal infections[10][11][12].
- FcRn blockers such as Vyvgart, Rystiggo and Imaavy treat the same disease a different way, by lowering antibody levels.
- Gefurulimab has not been compared head to head with any of these medicines; PREVAIL compared it only with placebo added to standard therapy[6].
- A person with myasthenia gravis can ask their neurologist how a weekly self-injected C5 blocker would fit their current treatment and which meningococcal vaccines a C5 blocker requires.
How Gefurulimab works
In generalized myasthenia gravis, antibodies attack the acetylcholine receptor where nerves signal muscles. That attack switches on complement, a part of the immune system that damages the muscle side of the nerve-muscle junction[6]. Gefurulimab blocks complement protein C5, so it cannot be split into the active pieces C5a and C5b that drive that damage[7].
Gefurulimab is built from nanobodies, very small antibody fragments first found in llamas and then adapted for people. The drug has 2 parts: the first binds C5 and the second binds albumin, a common blood protein, which keeps the drug in the body longer and allows once-weekly dosing[7][1]. The C5 blockers already approved for myasthenia gravis, Soliris, Ultomiris and Zilbrysq, target the same protein.
Clinical trial results
PREVAIL (NCT05556096) is a Phase 3, double-blind, placebo-controlled trial run at 113 sites in 20 countries. It randomized 260 adults with AChR antibody-positive generalized myasthenia gravis and an MG-ADL score of 5 or more to gefurulimab (131) or placebo (129) for 26 weeks, on top of their usual treatment, and 249 finished that period.
At week 26, MG-ADL scores (0 to 24, lower is better) fell 4.2 points on gefurulimab and 2.6 on placebo, a difference of 1.6 points (95% confidence interval 0.8 to 2.4). The doctor-measured QMG strength score fell 4.5 points against 2.4, a difference of 2.1 points. Improvement on MG-ADL appeared within 1 week[6]. The results were published in JAMA Neurology in September 2026[6], and a 105-week open-label extension continues[8]. A Phase 3 study in children with AChR antibody-positive generalized myasthenia gravis (NCT06607627) is recruiting[9].
Main registered trial: NCT05556096 on ClinicalTrials.gov. Check it for the current status, sites and contacts before asking about enrollment.
Side effects and safety
Gefurulimab has no US label yet, so the official side effects and warnings are not set. In PREVAIL, side effects were about as common on gefurulimab as on placebo[6]. AstraZeneca reported that the most common on gefurulimab were injection site reactions (9.9%), headache (9.9%) and back pain (7.6%)[5]. No meningococcal infections were reported during the 26-week trial[6].
All 3 C5 blockers approved for myasthenia gravis in the US carry a boxed warning for serious meningococcal infections[10][11][12]. Whether gefurulimab's label would carry the same warning is for the FDA to decide.
This is not a complete list of side effects. Talk to your doctor or pharmacist about what to expect and when to seek medical attention.
Taking Gefurulimab
In PREVAIL, people injected gefurulimab under the skin themselves: a weight-based loading dose on day 1, then weight-based doses once a week starting on day 8[8][1]. AstraZeneca describes the weekly self-injection as given with an autoinjector[1], and the EMA lists a 300mg solution in a prefilled pen or prefilled syringe[2]. The US dose would be set by the FDA label.
Development history
Alexion developed gefurulimab under the code ALXN1720[7]. AstraZeneca announced on July 24, 2025 that PREVAIL had met its main and secondary goals[4], presented full results on October 30, 2025[5], and the trial was published in JAMA Neurology in September 2026[6].
On September 17, 2026 the CHMP recommended approval of Klygefa in the EU as an add-on to standard therapy for adults with AChR antibody-positive generalized myasthenia gravis[2], and AstraZeneca said the next day that Klygefa is approved in Japan and other countries and that its US, China and other applications were under review[1]. AstraZeneca's results of October 30, 2026 list Klygefa among its first approvals of new medicines[3].
No European Commission decision had been announced as of November 7, 2026. The FDA had not announced a decision as of November 7, 2026.
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Common questions about Gefurulimab
▸What is Gefurulimab?
An investigational once-weekly injection under the skin for adults with generalized myasthenia gravis who test positive for antibodies against the acetylcholine receptor (AChR)[6]. AstraZeneca says its US application is under review, and no FDA decision date has been made public[1]. AstraZeneca says gefurulimab is approved in Japan and other countries, and on September 17, 2026 the European Medicines Agency's committee (CHMP) recommended EU approval under the brand name Klygefa[1][2]. In the Phase 3 PREVAIL trial, gefurulimab improved scores on the MG-ADL daily-living scale by 1.6 points more than placebo at week 26[6].
▸How does Gefurulimab work?
In generalized myasthenia gravis, antibodies attack the acetylcholine receptor where nerves signal muscles. That attack switches on complement, a part of the immune system that damages the muscle side of the nerve-muscle junction[6]. Gefurulimab blocks complement protein C5, so it cannot be split into the active pieces C5a and C5b that drive that damage[7]. Gefurulimab is built from nanobodies, very small antibody fragments first found in llamas and then adapted for people. The drug has 2 parts: the first binds C5 and the second binds albumin, a common blood protein, which keeps the drug in the body longer and allows once-weekly dosing[7][1]. The C5 blockers already approved for myasthenia gravis, Soliris, Ultomiris and Zilbrysq, target the same protein.
▸What are the side effects of Gefurulimab?
Gefurulimab has no US label yet, so the official side effects and warnings are not set. In PREVAIL, side effects were about as common on gefurulimab as on placebo[6]. AstraZeneca reported that the most common on gefurulimab were injection site reactions (9.9%), headache (9.9%) and back pain (7.6%)[5]. No meningococcal infections were reported during the 26-week trial[6]. All 3 C5 blockers approved for myasthenia gravis in the US carry a boxed warning for serious meningococcal infections[10][11][12]. Whether gefurulimab's label would carry the same warning is for the FDA to decide.
▸How is Gefurulimab taken?
In PREVAIL, people injected gefurulimab under the skin themselves: a weight-based loading dose on day 1, then weight-based doses once a week starting on day 8[8][1]. AstraZeneca describes the weekly self-injection as given with an autoinjector[1], and the EMA lists a 300mg solution in a prefilled pen or prefilled syringe[2]. The US dose would be set by the FDA label.
▸Is Gefurulimab FDA approved?
Not yet. Gefurulimab is under FDA review for Myasthenia Gravis; AstraZeneca (Alexion) has filed an application and a decision is pending. The FDA calendar page tracks the outcome.
▸Is gefurulimab FDA approved?
No. Gefurulimab is under FDA review and has no US approval.
Status: AstraZeneca said on September 18, 2026 that its US application is under review.
Decision date: AstraZeneca has not disclosed one.
Elsewhere: Gefurulimab is approved in Japan, and the CHMP recommended EU approval as Klygefa on September 17, 2026.
Source: AstraZeneca, September 18, 2026
▸What is Klygefa?
Klygefa is the brand name AstraZeneca uses for gefurulimab outside the US.
EU: The CHMP recommended approval of a 300mg injection in a prefilled pen or syringe.
US: There is no US brand name or approval yet.
▸How well did gefurulimab work in the PREVAIL trial?
Gefurulimab improved MG-ADL daily-living scores by 1.6 points more than placebo at week 26.
MG-ADL: Scores fell 4.2 points on gefurulimab and 2.6 on placebo.
QMG: The doctor-measured strength score fell 4.5 points against 2.4.
Timing: Improvement on MG-ADL appeared within 1 week.
▸How is gefurulimab different from Soliris, Ultomiris and Zilbrysq?
All 4 block complement protein C5, and no trial has compared them directly.
Schedule: Gefurulimab was given once a week under the skin; Zilbrysq is daily under the skin; Soliris is an IV infusion every 2 weeks; Ultomiris is an IV infusion every 8 weeks in adults.
Safety: The 3 approved drugs carry boxed warnings for serious meningococcal infections, and gefurulimab's US label has not been set.
Source: Gwathmey et al., JAMA Neurology 2026; FDA labels for Soliris, Ultomiris and Zilbrysq
Sources and references
Every factual claim on this page is drawn from the public sources listed below. Click any reference to open the original document.
- AstraZeneca · 2026-09-18. Klygefa (gefurulimab) recommended for approval in the EU by CHMP for the treatment of adults with generalised myasthenia gravis (gMG). https://www.astrazeneca.com/media-centre/press-releases/2026/klygefa-recommended-for-approval-in-the-eu.html
- European Medicines Agency · 2026-09-18. Klygefa | European Medicines Agency (EMA). https://www.ema.europa.eu/no/node/286753
- AstraZeneca · 2026-10-30. 9M and Q3 2026 results. https://www.astrazeneca.com/media-centre/press-releases/2026/9m-and-q3-2026-results.html
- AstraZeneca · 2025-07-24. Gefurulimab dual-binding nanobody demonstrated statistically significant and clinically meaningful improvement in functional activities of daily living in adults with generalised myasthenia gravis in PREVAIL Phase III trial. https://www.astrazeneca.com/media-centre/press-releases/2025/gefurulimab-nanobody-met-phase-iii-endpoints.html
- AstraZeneca · 2025-10-30. Gefurulimab demonstrates statistically significant and clinically meaningful improvement in Myasthenia Gravis Activities of Daily Living (MG-ADL) at week 26 with clinically meaningful improvement seen as early as week one in adults with gMG in PREVAIL Phase III trial. https://www.astrazeneca.com/media-centre/press-releases/2025/positive-results-from-prevail-phase-iii-trial-at-aanem-mgfa-scientific-session.html
- JAMA Neurology · 2026-09. Efficacy and Safety of Gefurulimab in Generalized Myasthenia Gravis: The PREVAIL Phase 3 Randomized Clinical Trial. https://pubmed.ncbi.nlm.nih.gov/42507440/
- Molecular Immunology · 2024. Characterization of the bispecific VHH antibody gefurulimab (ALXN1720) targeting complement component 5, and designed for low volume subcutaneous administration. https://pubmed.ncbi.nlm.nih.gov/38142486/
- ClinicalTrials.gov. Safety and Efficacy of ALXN1720 in Adults With Generalized Myasthenia Gravis. https://clinicaltrials.gov/study/NCT05556096
- ClinicalTrials.gov. PK, PD, Safety, and Efficacy Study of Gefurulimab in Pediatric Patients With AChR+ Generalized Myasthenia Gravis. https://clinicaltrials.gov/study/NCT06607627
- U.S. National Library of Medicine, DailyMed · 2026-07. SOLIRIS (eculizumab) injection, for intravenous use: prescribing information. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ebcd67fa-b4d1-4a22-b33d-ee8bf6b9c722
- U.S. National Library of Medicine, DailyMed · 2025-10. ULTOMIRIS (ravulizumab-cwvz) injection, for intravenous use: prescribing information. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=a9a590d9-0217-43c7-908d-e62a71279791
- U.S. National Library of Medicine, DailyMed · 2026-02. ZILBRYSQ (zilucoplan) injection: prescribing information. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=9f1d53d6-e495-4a3a-8bb9-680a15d25034