Sidhelo (donidalorsen) approved for on-demand treatment of hereditary angioedema attacks
FDA approved donidalorsen (Sidhelo; Kalvista Pharmaceuticals) oral tablets for on-demand treatment of acute attacks of hereditary angioedema (HAE) in adults and adolescents aged 12 and older. Donidalorsen is a plasma kallikrein inhibitor; the approval was supported by the ZENITH-1 phase 3 trial showing significant reduction in attack severity and time to symptom relief vs placebo. It is the first oral on-demand HAE therapy.
FDA approved donidalorsen (Sidhelo) ↗ on 9 October 2026 as the first oral on-demand therapy for acute hereditary angioedema (HAE) attacks in adults and adolescents ≥12 years. Donidalorsen is a small-molecule plasma kallikrein inhibitor that blocks bradykinin production. Prior oral HAE on-demand agents did not exist — patients relied on subcutaneous or IV administration. Full prescribing information is available on DailyMed ↗.
Hereditary angioedema — disease background
Hereditary angioedema (HAE) ↗ is an autosomal dominant disorder caused by deficiency or dysfunction of C1 inhibitor (HAE type I/II). C1-INH deficiency leads to uncontrolled activation of the contact system, generating plasma kallikrein which cleaves high-molecular-weight kininogen to produce bradykinin. Bradykinin causes vascular permeability leading to recurrent, unpredictable swelling of the skin, GI tract, and upper airway — laryngeal attacks can be life-threatening. Prevalence is approximately 1 in 50,000. The US Hereditary Angioedema Association ↗ and HAE International ↗ provide patient resources.
ZENITH-1 trial data
The phase 3 ZENITH-1 trial enrolled adults with HAE type I or II with a history of ≥3 attacks per 12 months. Patients were randomised to donidalorsen 300 mg oral tablet or placebo for acute attacks. Primary endpoint: time-weighted average symptom score over 4 hours (TWAS-4). Donidalorsen significantly reduced TWAS-4 vs placebo (p<0.001). Median time to meaningful symptom relief was approximately 1.5 hours with donidalorsen vs 4+ hours with placebo. Protocol registered at ClinicalTrials.gov NCT04594486 ↗. Pharmacology: kallikrein inhibition profile reviewed in NCBI kallikrein inhibitor review ↗.
Place in therapy and prescribing context
The HAE treatment landscape now includes both subcutaneous prophylaxis (lanadelumab/Takhzyro, berotralstat/Orladeyo ↗) and on-demand options. Donidalorsen is positioned as oral on-demand therapy — practical for patients who cannot self-inject or prefer oral treatment. Prescribers should note that patients should still have injectable rescue therapy available for severe or laryngeal attacks. AAAAI HAE patient education ↗ provides guidance on when to seek emergency care.
FAQ
What does FDA approval mean?
FDA approval means the agency has determined, based on scientific evidence submitted by the manufacturer, that a drug's benefits outweigh its known risks for a specific indication and patient population. The review process includes evaluation of clinical trial data, manufacturing quality, and proposed labelling. See the FDA drug approval process overview ↗.
Does approval mean the drug is available immediately?
Not always. Commercial launch timelines depend on manufacturing scale-up, pricing, and distribution. REMS-restricted drugs ↗ require prescriber or pharmacy enrolment before the product can be dispensed. Rare disease drugs may also have limited initial supply. Check the manufacturer's website or RxNav ↗ for availability status.