Approved despite lack of evidence of efficacy
The muscular dystrophies are an inherited group of progressive myopathic disorders caused by mutations in a number of genes needed for normal muscle function. Duchenne muscular dystrophy (DMD) is caused by mutations in the dystrophin gene and is associated with the most severe signs and symptoms.1
Characterized by a progressive loss of muscle mass and strength, DMD almost always affects boys. Initial signs and symptoms are usually evident between ages 3 and 5 years and worsen over time. Most patients are nonambulatory by their early teens and face life-threatening cardiopulmonary complications as the disease worsens. Most patients with DMD die in their 20s or 30s.2,3
Some genetic mutations in DMD involve the deletion of certain exons, which are gene segments containing information needed for protein synthesis.4 Eteplirsen (Exondys 51, Sarepta) is an antisense oligonucleotide designed to bind to exon 51 of dystrophin pre-messenger RNA (pre-mRNA), resulting in exclusion of this exon (exon skipping) during mRNA processing.5 Exon skipping is designed to allow production of a partially functional dystrophin protein.
Eteplirsen is indicated for pediatric and adult patients who have a confirmed mutation of the dystrophin gene amenable to exon 51 skipping, which affects about 13% of patients with DMD.2 Administered I.V., eteplirsen is the first drug to be approved to treat patients with DMD.
Eteplirsen was approved under the FDA's accelerated approval program, even though its clinical benefit hasn't been established. The primary study evaluating the new drug included a 6-minute walk test as a clinical outcome measure. No significant difference in the distance walked in 6 minutes was found between patients treated with eteplirsen and those receiving placebo. Continued approval may be contingent on verification of a clinical benefit in confirmatory trials.5
Precautions: Eteplirsen has no labeled contraindications. It hasn't been studied in pregnant or lactating women, or in patients with renal or hepatic impairment.
Adverse reactions: balance disorder, vomiting, contact dermatitis
Supplied as: single-dose vials containing 100 mg/2 mL (50 mg/mL) and 500 mg/10 mL (50 mg/mL) of the drug
Dosage: 30 mg/kg once a week via I.V. infusion over 35 to 60 minutes
Nursing considerations: (1) Before preparing doses, allow vials to warm to room temperature. (2) Invert, but don't shake, vials two or three times. Dilute the prescribed drug dose with 0.9% Sodium Chloride Injection to a total volume of 100 to 150 mL. See the prescribing information for complete instructions for preparation and administration. (3) Before eteplirsen administration, a topical anesthetic cream may be applied to the infusion site. (4) The infusion should be completed within 4 hours of dilution. If not used immediately, the diluted solution may be stored for up to 24 hours in a refrigerator. (5) Store vials in a refrigerator and protect from light. (6) Inform patients that they may experience transient erythema, facial flushing, and elevated temperature on the days they receive the drug.
1. Darras BT. Clinical features and diagnosis of Duchenne and Becker muscular dystrophy. UpToDate. 2016. http://www.uptodate.com
2. FDA grants accelerated approval to first drug for Duchenne muscular dystrophy. Food and Drug Administration. News release. September 19, 2016.