The Food and Drug Administration has approved a new oral drug, risdiplam (Evrysdi), to treat spinal muscular atrophy (SMA) in patients two months of age and older. SMA is a group of hereditary diseases that damages and kills motor neurons, which are specialized nerve cells in the brain and spinal cord. Motor neurons control movement in the arms, legs, face, chest, throat, and tongue, as well as skeletal muscle activity, including speaking, walking, swallowing, and breathing. Risdiplam is the second drug approved to treat SMA and the first oral drug. Risdiplam treats SMA symptoms but does not cure the disease.

Risdiplam was approved based on an open-label study of 21 patients with SMA who were at an average age of 6.7 months at the start of the study. After 12 months of treatment, 41% of infants were able to sit independently for more than five seconds, unlike almost all untreated infants, who could not sit independently. After 23 or more months of treatment, 81% of patients were surviving without permanent ventilation, which is not the typical progression of the disease in untreated patients. Risdiplam was also tested in those with later-onset SMA. That study was a randomized, placebo-controlled trial of 180 patients ages two to 25 years. After one year of treatment, the motor function scores of patients given risdiplam had improved, compared with those of patients given placebo, which decreased.

For those patients with later-onset disease, the most common adverse effects from risdiplam were fever, diarrhea, and rash. Patients with infantile-onset disease most commonly experienced upper respiratory tract infection, pneumonia, constipation, and vomiting.

Risdiplam should not be coadministered with substrates of multidrug and toxin extrusion transporters because risdiplam can increase the plasma concentration of these drugs (metformin, for example). Nurses should use a drug database to determine potential drug interactions.

Risdiplam should be reconstituted for the patient by the pharmacist. Nurses should teach parents or patients to administer the drug daily after a meal or after breastfeeding, but not to mix it in formula or milk. Risdiplam should be administered with the reusable oral syringe that comes with the drug.

For complete prescribing information for risdiplam, see http://www.accessdata.fda.gov/drugsatfda_docs/label/2020/213535s000lbl.pdf.