Results from a small clinical trial have shown that drugs that are usually prescribed for erectile dysfunction — sildenafil (Viagra) and tadalafil (Cialis) — might be able to reduce some of the symptoms of Duchenne MD.
In Duchenne MD, the essential muscle protein “dystrophin” is not produced. The main purpose of this protein is to protect muscles from damage during contraction. In addition, studies in mice have shown that without dystrophin, blood vessels supplying muscles do not adequately dilate during exercise, resulting in muscle fatigue and weakness. In mice this can be reversed with drugs such as sildenafil and tadalafil.
The results of a small clinical trial involving 10 boys with Duchenne MD were published this month. The boys aged between 8 and 13 years had the blood flow in their forearm muscles measured as they carried out handgrip exercises. Their blood flow was compared with 10 similarly aged healthy boys, which confirmed that those with Duchenne MD had reduced blood flow.
The boys with Duchenne MD then took a dose of sildenafil or tadalafil and their forearm blood flow was measured. Two weeks later those that had taken sildenafil took tadalafil and vice versa and the tests were repeated. It was found that after treatment with either drug they had the same blood flow response as the healthy boys during exercise. A similar result was obtained in a previous clinical trial of tadalafil for Becker MD (a milder form of Duchenne MD). It is important to note that a trial of sildenafil (Viagra) for Duchenne and Becker MD was started in 2010 to investigate whether it could treat the heart problems associated with these conditions. Unfortunately it was suspended in 2013 due to a negative impact on heart function. As a result, future studies will need to carefully monitor the impact of this type of drug on the heart.
Although the team’s findings are encouraging, a lot more research needs to be done before these types of drug can be recommended for individuals with Duchenne and Becker MD. Crucially it is not known if increasing blood flow preserves muscle strength and slows disease progression and if long-term use of this type of drug is safe. In order to address these questions a phase 3 clinical trial of tadalafil for Duchenne MD has started recruiting participants. The trial aims to recruit over 300 boys with Duchenne MD in 16 countries (not Australia) and will include functional tests like the 6 minute walk test.
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• The MDA Duchenne and Becker MD factsheets contain more information about the condition including a research summary
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This research was published in the journal Neurology and can only be downloaded after paying a fee. The article is written in technical language with no summary in lay terms.
Nelson MD et al. PDE5 inhibition alleviates functional muscle ischemia in boys with Duchenne muscular dystrophy. Neurology. 2014 May 7.
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Uploaded 13 May 2014