High distribution of azide in blood investigated in vivo, and its stability in blood investigated in vitro

We investigated the distribution of azide in blood and solid tissues in rats that were orally administered with fatal or toxic doses of sodium azide. We also determined the stability of azide in human blood in vitro. Azide concentrations were measured by gas chromatography–mass spectrometry after pentafluorobenzyl derivatization. The rats died immediately after administration of 100 mg sodium azide per kilogram of body weight. Azide was detected in blood and stomach at concentrations of >100 μg/ml, with lower concentrations in solid tissues, such as the liver, kidney, heart, and lung. The rats survived after administration of 25 mg sodium azide per kilogram of body weight. Azide was detected in blood until 3 h after administration. These results suggest that blood is the most useful specimen for detecting azide poisoning. We conducted in vitro experiments for the stability of azide by spiking it into human blood collected from healthy volunteers. After spiking human blood with 5 μg/ml of sodium azide, the azide concentration decreased in the red blood cell fraction, but not in the plasma fraction at 4 °C. We investigated the disappearance of azide from red blood cells using hemoglobin molecules with different heme oxidation and ligand binding states at 23 °C. The azide concentration was unaffected by carboxyhemoglobin or methemoglobin, but was decreased to 30 % of the original level by oxyhemoglobin. The disappearance of azide in the presence of oxyhemoglobin was suppressed by methemoglobin, but not by cyanmethemoglobin. These results suggest that azide is oxidized by oxyhemoglobin, and is stabilized by methemoglobin via strong ligand binding.