Evrysdi™ (risdiplam) is the first and only oral medication indicated for the treatment of spinal muscular atrophy (SMA) in patients of two months of age and older.
The drug was developed by Genentech, a member of the Roche Group, in partnership with the SMA Foundation and PTC Therapeutics.
Evrysdi (risdiplam) is available as an oral solution with a maximum dose of 5mg administered once daily, directly distributed to patients’ homes in the US by Accredo Health Group, a speciality pharmacy.
The new drug application (NDA) for Evrysdi (risdiplam) was submitted to the US Food and Drug Administration (FDA) in September 2019, and accepted for priority review in November 2019.
FDA approved Evrysdi (risdiplam) for the treatment of SMA in adults and children two months of age and older in August 2020. The drug obtained the orphan drug designation in January 2017, while the fast track designation was granted by the FDA in April 2017.
European Medicines Agency (EMA) granted the PRIME (PRIority MEdicines) and orphan drug designations to risdiplam in December 2018 and February 2019, respectively.
Spinal Muscular Atrophy (SMA) causes and symptoms
Spinal Muscular Atrophy (SMA) is a serious, progressively fatal neuromuscular disorder, affecting around one in every 10,000 infants, the main genetic cause of child mortality.
SMA is caused by a survival motor neuron 1 (SMN1) gene mutation, which results in SMN protein deficiency.
The protein is present in the body and is significant to the nerve system, which regulates muscles and movement. Nerve cells cannot function properly without the protein, leading to muscle fatigue.
SMA is classified into four main types of SMA (1, 2, 3, and 4) based on the disease’s intensity and the age when symptoms start. The physical strength of a person and their ability to walk, eat, or breathe may be greatly diminished or destroyed, depending on the type of SMA.
Severity of the disease is also associated with the number of copies of the SMN2 gene in each individual.
Risdiplam mechanism of action
Risdiplam is a splicing modifier of motor neuron 2 (SMN2) designed to treat patients with spinal muscular atrophy (SMA) caused by chromosome 5q mutations leading to SMN protein deficiencies.
The drug demonstrated a significant increase in exon 7 inclusion in SMN2 messenger ribonucleic acid (mRNA) transcripts and the production of full-length SMN protein in the brain during in vitro assays and studies in transgenic animal models of SMA.
In vitro and in vivo results suggest that risdiplam can induce alternate splicing of additional genes, including FOXM1 and MADD.
FOXM1 and MADD are believed to be active in the control of cell cycles and apoptosis, respectively, identified as potential contributors to adverse reactions seen in animals.
Safety and effectiveness of risdiplam in children under two months of age are currently unknown.
Clinical trials on Evrysdi
FDA approval of Evrysdi was based on the results from two clinical studies FIREFISH with infantile-onset SMA and SUNFISH with later-onset SMA.
FIREFISH (Study 1) was an open-label, multicentre, pivotal, and two-part clinical study including 21 patients in part 1 and 41 patients in part 2. The dose for part 2 was determined in part 1.
SUNFISH (Study 2) was also a two-part, multicentre trial enrolling 51 patients in part 1 and 180 patients in part 2. Part 1 was an exploratory dose-finding study, while part 2 was a randomised, double-blind, and placebo-controlled pivotal study.
Study 1 enrolled infants (aged 2 to 7 months) with type 1 SMA while Study 2 included patients (aged 2 to 25 years) with type 2 and 3 SMA.
“In vitro and in vivo results suggest that risdiplam can induce alternate splicing of additional genes, including FOXM1 and MADD.”
In FIREFISH part 1 study, the efficacy was based on the survival without permanent ventilation and sitting without support for at least five seconds at 12 months of treatment measured by the Gross Motor Scale of the Bayley Scales of Infant and Toddler Development Third Edition (BSID-III).
Patients were administered with the recommended Evrysdi dose of 0.2 mg / kg / day. Approximately 41% of the patients were able to sit comfortably for around five seconds (BSID-III, gross motor scale) after 12 months of treatment.
After 12 months of Evrysdi treatment, 90% of the patients were alive without permanent ventilation and reached the age of 15 months or older.
After a minimum of 23 months of Evrysdi treatment, 81% of all patients (median age of 32 months) were alive without permanent ventilation.
In SUNFISH part 2 study, the primary endpoint was mean change from baseline in the motor function measure (MFM-32) total score after 12 months of treatment with Evrysdi when compared to placebo.
Patients treated with Evrysdi reported a significantly greater change in motor function (n=115) from baseline to placebo (n=60), as assessed by MFM-32.
At month 12, patients on Evrysdi saw an average 1.36 increase in their MFM-32 score, compared to a 0.19 decrease in placebo patients (inactive treatment).
The percentage of patients treated with Evrysdi who had a total score change of three or more in baseline MFM-32 was 38.3% when compared to 23.7% for placebo.
Evrysdi treatment also improved upper limb motor function in children and adults compared to the baseline, as measured by the Revised Upper Limb Module (RULM), a secondary endpoint of the study.
Common adverse reactions observed during the studies were diarrhoea, fever, and rash in later-onset SMA (SUNFISH) and pneumonia, upper respiratory tract infection, vomiting and constipation in FIREFISH (infantile-onset SMA).