This study is designed to assess the efficacy, safety, tolerability, and pharmacokinetics (PK) of AVI-4658 (eteplirsen) in both 50.0 mg/kg and 30.0 mg/kg doses administered over 24 weeks in subjects diagnosed with Duchenne muscular dystrophy (DMD).

For details regarding the roll-over extension study 4658-us-202, please refer to NCT01540409.

Major Inclusion and Exclusion Criteria:

Inclusion Criteria:

A subject must meet all of the following criteria to be eligible for this study.

• Be a male with DMD and have an out-of-frame deletion(s) that may be corrected by skipping exon 51 [e.g., deletions of exons 45-50, 47-50, 48-50, 49-50, 50, 52, 52-63], as confirmed in a Clinical Laboratory Improvement Act-accredited laboratory by any of the peer-reviewed and published methodology that evaluates all exons (including, but not limited to, multiplex ligation-dependent probe, comparative genomic hybridization, and single condition amplification/internal primer analysis).
• Be between the ages of 7 and 13 years, inclusive.
• Have stable cardiac function and stable pulmonary function (forced vital capacity [FVC] ≥50% of predicted and not require supplemental oxygen) that, in the Investigator's opinion, is unlikely to decompensate over the duration of the study.
• Be receiving treatment with oral corticosteroids and have been on a stable dose for at least 24 weeks before study entry. Subjects may be allowed to take other (non-RNA antisense or gene therapy) medication (including angiotensin-converting enzyme [ACE] inhibitors, β blockers, losartan potassium, and coenzyme Q) as long as they have been on a stable dose of the medication for 24 weeks before the screening visit (Visit 1) and the dose will remain constant throughout the study.
• Have intact right and left biceps muscles or an alternative upper arm muscle group.
• Achieve an average distance within 200m and 400m ±10% (i.e. within 180m and 440m) while walking independently over six minutes.
• Have a left ventricular ejection fraction (LVEF) of >40% based on the ECHO that is obtained at the screening visit (Visit 1). A subject who has abnormal ECHO findings but who has an LVEF of >40% may be enrolled in the study at the Investigator's discretion; however, the subject must have been receiving stable doses of ACE inhibitors or β blockers for at least 24 weeks before study entry.
• Have a parent(s) or legal guardian(s) who is able to understand and comply with the all of the study procedure requirements.
• Be willing to provide informed assent and have a parent(s) or legal guardian(s) who is willing to provide written informed consent for the subject to participate in the study.

Exclusion Criteria:

A subject who meets any of the following criteria will be excluded from this study.

• Use of any pharmacologic treatment, other than corticosteroids, that might have an effect on muscle strength or function within 12 weeks before study entry (e.g., growth hormone, anabolic steroids).
• Previous treatment with the experimental agents eteplirsen, BMN-195, or PRO051.
• Previous treatment with any other experimental agents or participation in any other DMD interventional clinical study within 12 weeks before entry into this study; including use of the shock training system or "STS," or planned use during this study.
• Surgery within 3 months before study entry or planned surgery at any time during this study.
• Presence of other clinically significant illness at the time of study entry, including significant renal dysfunction (as measured by urinary cystatin C, KIM-1, or urinary total protein), or average heart rate during screening Holter monitoring in excess of 110 bpm (unless subsequently treated and confirmed controlled and stable on a β-blocker) or QTc >450 ms.
• Use of any aminoglycoside antibiotic within 12 weeks before the screening visit (Visit 1) or need for use of an aminoglycoside antibiotic during the study (unless discussed and agreed with the Principal Investigator and medical monitor).
• Prior or ongoing medical condition that, in the Investigator's opinion, could adversely affect the safety of the subject or that makes it unlikely that the course of treatment or follow-up would be completed or could impair the assessment of study results.

24 weeks

Due to the small number of study participants, a single adverse event (AE) in 1 patient exceeds the reporting threshold of 5%. Refer to the "Post-Hoc Outcome Measures" #4 and #5 for a summary of frequent and related AEs.