The effect of hyperbaric helium-oxygen on the acute toxicity of several drugs

The effect of a hyperbaric helium-oxygen environment on drug toxicity was investigated in the following systems: (1) The intravenous lethal doses of pentobarbital, lidocaine, and ethanol in rats; (2) the intravenous LD50 for morphine in rats; and (3) the oral toxicity of an LD50 dose of aspirin in mice. Except for mice given aspirin, restrained, unanesthetized animals were equilibrated with the atmosphere (19.2 atm abs. helium-0.2 atm abs. oxygen, equivalent to the pressure at a depth of 600 feet) for 45 min in a hyperbaric chamber. Animals were then injected remotely via indwelling jugular vein catheters. The lethal dose of pentobarbital, lidocaine, or ethanol was determined by slow intravenous infusion to the point of respiratory arrest. The LD50 of morphine was determined from the mortality 2 hr after injection. Mice were injected orally with a suspension of aspirin in sodium alginate and pressurized rapidly; the mortality was determined 3 hr later. For each drug, control animals were treated in exactly the same manner as pressurized animals. In the case of every drug examined, the toxicity observed during exposure to the hyperbaric environment did not differ significantly from that under normal pressure.