The experimental drug tirasemtiv has shown promise in a phase 2a clinical trial in 32 people with myasthenia gravis (MG). Improvements in general and respiratory muscle function occurred in response to the medication.
Six hours after receiving a single, oral dose of tirasemtiv, study participants showed improvements on a standardized scale of MG severity (the Quantitative MG score) and in forced vital capacity, a measurement of respiratory function.
The improvements were proportional to the dose taken, which was either a placebo, 250 milligrams of tirasemtiv or 500 milligrams of tirasemtiv.
The two doses tested were each well-tolerated, and there were no premature trial terminations or serious adverse events. The most commonly reported side effect was dizziness, which increased in frequency with the dose. Dizziness was reported as "mild" in all cases except one, which was reported as "moderate."
Cytokinetics, developer of tirasemtiv, announced the findings in a Nov. 26, 2012, press release. The data "suggest that tirasemtiv may have the potential to meaningfully improve the lives of patients with myasthenia gravis and other neuromuscular diseases," said Duke University neurologist Donald Sanders, who chairs the Tirasemtiv in Myasthenia Gravis Study Group.
Tirasemtiv — formerly known as CK-2017357— is designed to increase the sensitivity of muscle fibers to calcium, thereby increasing skeletal muscle force in response to input from the nervous system, and decreasing muscle fatigue.
For a video of the drug's proposed mechanism of action, see Skeletal Muscle Contractility on the Cytokinetics website.
The drug also is being evaluated for the treatment of amyotrophic lateral sclerosis (ALS) and other conditions. A phase 2b trial in ALS is under way, following encouraging results from earlier studies.