"severely poisoned" is correct and usable in written English.
You can use it to describe someone or something that has been poisoned to a dangerous or life-threatening degree. For example: "The patient had been severely poisoned and was on the brink of death."
Some of the subjects were severely poisoned; they twitched, vomited, and had trouble breathing.
Death may come within a day, although people less severely poisoned may live for a week.
Most of her internal organs were severely poisoned by toxins released by the bacteria, and she suffered serious muscle damage.
One crewmember was so severely poisoned that the Army decided to study him; no American exposed to the chemical had ever come so close to death.
According to an internal memorandum issued in mid-August, the agency will no longer prohibit the sale of PCB-contaminated land unless the property is severely poisoned.
But not three days later came a dispatch from a town 55 miles southeast of Mengxi Village: 103 children and 26 adults were found to be severely poisoned by lead pollution from tinfoil processing plants, according to China's official Xinhua news agency.
Sulfur severely poisons the Au/TiO2 catalyst, which is irreversible over time-on-stream under high pressure (21 bar) WGS conditions.
We recommend that oxygen is provided as soon as possible to all moderate-to-severely poisoned patients but that its absence does not slow or prevent the provision of atropine.
Presence of trimethylamine in the electrolyte solution also severely poisons a Cu electrode in the CO2 reduction.
However, CuO was found to severely poison the precious metal (PGM) functions in the filter, dramatically reducing its CO/HC oxidation activity.
Carbonyl sulfide and particularly sulfur dioxide severely poison all the catalysts investigated due to the strong adsorption of the sulfur compounds and active site blockage.
