(Adds analyst comments; updates shares)
Nov 21 (Reuters) - Cytokinetics Inc shares plummeted nearly 28 percent on Tuesday after the drugmaker said it would stop developing one of its treatments for ALS, a fatal neuro-degenerative disorder, after the drug failed to improve lung function in a key trial.
Amyotrophic lateral sclerosis, also called Lou Gehrig's disease, is a condition that affects nerve cells in the brain and the spinal cord, with deaths and disability in patients mainly caused by respiratory failure.
The condition, whose sufferers include renowned British physicist Stephen Hawking, attracted international attention in 2014 with the "Ice Bucket Challenge," in which people posted videos of pouring ice-cold water on themselves to encourage donations to research.
Cytokinetics said its drug, tirasemtiv, failed to show a statistical significant difference, when compared with a placebo, in lowering what is called slow vital capacity of the lungs, or the volume of air expelled without force.
The drugmaker said more patients on tirasemtiv dropped out of the late-stage trial, than patients on a placebo, due to certain side effects.
Cytokinetics said it would focus on its second drug for ALS, CK-2127107, that has shown to have a better tolerability profile.
While tirasemtiv's high dropout-rate was due to side effects such as dizziness, they would likely not be felt with the other drug, analysts said.
CK-2127107 was designed as a follow-on compound to tirasemtiv, Needham analyst Chad Messer said, adding that the drug was designed not to cross the blood-brain barrier therefore avoiding the dizziness caused by tirasemtiv.
Both tirasemtiv and CK-2127107 are designed to use the fast skeletal muscle troponin activator mechanism that can improve muscle function in ALS patients.
The profile of second-generation CK-2127107 has a better chance of demonstrating improvements, Piper Jaffray analyst Charles Duncan said.
Cytokinetics Chief Executive Robert Blum was also confident on the prospects of its second drug, which the company is developing in collaboration with Japan's Astellas Pharma Inc .
"We believe CK-2127107 will be better tolerated and potentially more effective than tirasemtiv," Blum said in a statement.
Mitsubishi Tanabe Pharma Corp's ALS drug was the first to win regulatory approval in the United States in more than two decades in May.
Cytokinetics' shares were at $8.02 in afternoon trading, down about 27.7 percent, after touching a one-and-a-half year low of $7. (Reporting by Divya Grover in Bengaluru; Editing by Savio D'Souza and Anil D'Silva)