Figure 2.

Effects of cobinamide and hydroxocobalamin on tissue oxyhemoglobin, deoxyhemoglobin, and total hemoglobin concentrations in representative cyanide-poisoned rabbits. Changes in tissue oxyhemoglobin (OHb), deoxyhemoglobin (RHb), and total hemoglobin (THb) as measured by DOS are shown during and following cyanide infusion in individual rabbits. The decrease in deoxyhemoglobin concentration during 60 min of cyanide infusion is due to the inability of tissues to remove oxygen from circulating blood, leaving more hemoglobin in the oxygenated state. At 60 min, when the cyanide infusion was stopped, the animals received either 5 cc of saline (a), 5 cc of 16.3 mM cobalamin in saline (b), or 5 cc of 16.3 mM cobinamide in saline (c). In the control animal, oxy- and deoxyhemoglobin concentrations gradually returned toward baseline after the cyanide infusion was discontinued but never fully returned to preinfusion values. In the hydroxocobalamin-treated animal, oxy- and deoxyhemoglobin concentrations returned to baseline at ∼130 min, i.e., 70 min following drug administration. In contrast, oxy- and deoxyhemoglobin concentrations returned to baseline within 10 min following cobinamide administration.