Duchenne muscular dystrophy (DMD) is a genetic disorder affecting 1 in 5,000 males which causes progressive muscle deterioration, loss of mobility and eventual death, with an average lifespan of around 25 years. While no cure currently exists for DMD, a novel treatment known as antisense-mediated exon skipping therapy has shown great promise. Exon skipping therapy induces the skipping of mutated exons, restoring the reading frame in dystrophin transcripts and resulting in a truncated but partially functional protein product. In February 2021, Sarepta Therapeutics received accelerated Food and Drug Administration (FDA) approval for their new antisense oligonucleotide, casimersen (brand name Amondys 45). Casimersen targets exon 45 of the dystrophin gene and is expected to treat ~8% of the DMD patient population. The continued approval of this drug will be dependent on satisfactory clinical results from an ongoing phase III trial. This article summarizes the preclinical and clinical data currently available for casimersen, emphasizing pharmacokinetics and safety.