Eteplirsen (Exondys 51) is an antisense oligonucleotide designed to induce exon 
51 skipping that is developed by Sarepta Therapeutics. Intravenous eteplirsen 
has received accelerated approval from the US FDA for the treatment of Duchenne 
muscular dystrophy (DMD) in patients with a confirmed mutation of the DMD gene 
amenable to exon 51 skipping. Eteplirsen has orphan drug designation in the USA 
and EU, and rare paediatric disease designation in the USA for use in DMD. In 
the phase III PROMOVI trial, eteplirsen significantly increased dystrophin 
levels from baseline in muscle tissues of 12 evaluable patients with DMD after 
48 weeks of treatment. This finding is supported by data from phase II trials. 
Long-term treatment with eteplirsen was associated with a decrease in the rate 
of decline in ambulation and pulmonary function in an open-label extension of a 
phase II trial. Eteplirsen was generally well tolerated in clinical trials. This 
article summarizes the milestones in the development of eteplirsen leading to 
this first approval for DMD.