U.S. regulators have cleared the way for a Canadian drug developer to test its experimental Ebola treatment on some infected patients, raising new hope in the Ebola outbreak in Africa and sending the company's share price soaring.

Burnaby, B.C.-based Tekmira Pharmaceuticals Corp. had begun trials on a drug called TKM-Ebola, designed to "silence" disease-causing genes in the Ebola virus.

After healthy patients began taking it as part of the first phase of a clinical trial, the U.S. Food and Drug Administration (FDA) put a clinical hold on the drug to explore possible side effects that emerged. But Tekmira announced late Thursday that the FDA has agreed to change its dictate to a partial hold, paving the way for the drug to be administered to infected Ebola patients whose lives are at risk.

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World health authorities are on high alert over an outbreak of the deadly Ebola virus in three West African countries. Nigerian President Goodluck Jonathan declared a national state of emergency on Friday, as the World Health Organization warned the Ebola crisis is likely to worsen.

"We are pleased that the FDA has considered the risk-reward of TKM-Ebola for infected patients," Tekmira's president and CEO, Mark Murray, said in a statement. "We have been closely watching the Ebola virus outbreak and its consequences, and we are willing to assist with any responsible use of TKM-Ebola."

Tekmira's stock rose 47.3 per cent to $23 on the Toronto Stock Exchange on Friday, once news of the FDA's clearance was disclosed after trading ended on Thursday.

The drug has yet to be proven to work on humans, but produced 100-per-cent protection from otherwise lethal doses of the Ebola virus when used to treat non-human primates. The company is developing its experimental Ebola treatment under a $140-million (U.S.) contract with the U.S. Department of Defence, and the FDA gave it a "Fast Track" designation in March.

A spokesperson for the FDA, Stephanie Yao, said the agency cannot discuss specific products as they are considered confidential under U.S. law and FDA regulations. But she said clinical holds are based on risk-benefit assessments, and that a patient with a disease might have a different risk-benefit balance than a healthy patient.

"If the benefits of studying the product on an individual outweigh the risks, we may consider permitting that study to proceed," Ms. Yao said in an e-mail.

Another experimental drug that benefited from Canadian research has already been administered to two American aid workers infected with Ebola while caring for patients in Liberia. ZMapp, a new drug in development by San Diego-based Mapp Biopharmaceutical, contains two antibodies developed at a Public Health Agency of Canada lab in Winnipeg. Mapp could not be reached for comment.

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Trials of TKM-Ebola on healthy patients are still on hold for the time being, and Mr. Murray's statement said his company is "focused on an expedient resolution of this." A Tekmina spokesperson declined a request for an interview.

Meanwhile, it is still unclear how effective these new drugs might be for infected humans, or how quickly doses could be made and deployed. But with health officials putting the current death rate from the new outbreak of the virus at around 70 per cent, the FDA clearance gives a potentially life-saving drug a path out of the laboratory.

"We recognize the heightened urgency of this situation, and are carefully evaluating options for use of our investigational drug within accepted clinical and regulatory protocols," Mr. Murray said in his statement.

With files from Reuters and The Canadian Press