The supplies of some drugs required to keep COVID-19 patients on ventilators are low enough that hospitals in Ontario are taking steps to conserve their use.

While hospitals say they are not facing an immediate shortage, the rate at which the most severely ill COVID-19 patients consume the drugs is raising fears that the existing supply of certain medications will run out in a matter of weeks.

"Certainly the potential is there for some very significant shortages in these medications," said Christina Adams, chief pharmacy officer of the Canadian Society of Hospital Pharmacists.

"Because we're seeing two to three times increase in the demand for these drugs, our [national] supply may only last a month or two before we really need to start looking at alternatives for resupply," Adams said Tuesday in an interview with CBC News.

When putting someone on a ventilator, certain medications are crucial to sedate and immobilize the patient, and COVID-19 patients seem to require more of these drugs than other ventilated patients, says Damon Scales, chief of critical care medicine at Sunnybrook Health Sciences Centre in Toronto.

"The whole world wants these same medications to provide the same therapy, so this is a real concern," Scales said.

Patients on ventilators must be deeply sedated and their chest muscles immobilized to prevent lung damage from the mechanical ventilation, said Scales.

"We need to take the human being out of the equation so the machine and my team can do the work they need to do to help prevent the respiratory failure from worsening," he said.

According to the medical experts interviewed for this story, the specific drugs most at risk of shortage right now include:

propofol (a sedative).

cisatracurium (a paralytic, or neuromuscular blocker).

rocuronium (a paralytic, or neuromuscular blocker).

All three are on a Health Canada list current drug scarcities with "the greatest potential impact on Canada's drug supply and health care system."

Individual hospitals are taking steps to preserve their supplies, such as choosing other medications for non-COVID patients, said Jin Huh, senior director of pharmacy for the University Health Network in Toronto.

"We've been working with the government, provincially as well as federally, as well as purchasing organizations to get a better understanding what the supply is out there and how quickly we could ramp up that supply," said Huh.

Medical sources tell CBC News the province has assigned health officials to tally the existing stocks of certain drugs at hospitals, to develop guidelines for conserving these medications and to identify wider sources of supply.

Ontario is working with pharmaceutical companies on the issue, said Health Minister Christine Elliott.

"We're prepared to go and negotiate with other countries as well to get the active ingredients that we need in order to make these medications, because we know that there is going to be demand for them," Elliott said in response to a question at a news conference Tuesday.

A provincial group focused on critical care in the COVID-19 pandemic is "actively working with the Ministry [of Health] to identify and address local drug supply issues and to coordinate appropriate responses across Ontario hospitals," added Elliott's director of media relations, Hayley Chazan, in a later email to CBC News.

The hope is that physical distancing measures continue to rein in the spread of the virus enough to give time to build up the drug supply.

"The longer we can give the health system the ability to to ramp up production and to be able to cope with this potential surge in patients the better off we'll be," said Adams.

There's potentially good news on this in provincial statistics that show the number of COVID-19 patients on ventilators in hospital intensive care units has dipped slightly in the past week and remains far lower than what modellers projected could be the case for mid-April.