Summary for Patients: This study, funded by the Muscular Dystrophy Association, is intended
to build on recent findings published in the journal Nature showing beneficial effects of
tadalafil (also known as Cialis) in mice with an animal version of Duchenne and Becker
muscular dystrophies. Only two doses of tadalafil improved muscle blood flow, allowing the
dystrophic mice to perform more exercise with less muscle injury. This new short-term
clinical trial will move the testing from animals to human patients with Becker muscular
dystrophy and examine the effects of acute tadalafil dosing on muscle blood flow during a
bout of exercise. Patients will take two doses of tadalafil prior to exercising. Then doctors
will measure whether muscles receive increased blood flow and therefore are better protected
during exercise.
Scientific Hypothesis: In patients with Becker muscular dystrophy (particularly those with
dystrophin gene mutations between exons 41-46), loss of sarcolemmal nitric oxide synthase
engenders functional muscle ischemia and thus muscle edema after an acute bout of exercise.
The investigators further hypothesize that PDE5A inhibition, which boosts nitric oxide-cGMP
signaling, constitutes an effective new countermeasure for these patients.