Uptake and Distribution of the Abused Inhalant 1,1-Difluoroethane in the Rat

Joseph Avella^1,2, Naveen Kunaparaju¹, Sunil Kumar¹, Michael Lehrer³, S. William Zito¹, and Michael Barletta^1
1Department of Pharmaceutical Sciences, St. John’s University, Jamaica New York; ²Department of Health Services, Office of the Chief Medical Examiner, Nassau County, New York; and ³Department of Health Services, Division of Medical-Legal and Forensic Investigations, Suffolk County, New York

1,1-Difluoroethane (DFE) is a halogenated hydrocarbon used as a propellant in products designed for dusting electronic equipment and air brush painting. When abused, inhaled DFE produces intoxication and loss of muscular coordination. To investigate DFE toxicokinetics, groups (n = 3) of Sprague-Dawley rats were exposed to 30 s of 20 L/min DFE. The experimental model was designed to mimic exposure during abuse, a protocol which has not been conducted. Tissue collection (blood, brain, heart, liver, and kidney) occurred at 0, 10, 20, 30, 45, 60, 120, 240, 480, and 900 s. Average peak DFE levels were blood 352, brain 519, heart 338, liver 187, and kidney 364 mg/L or mg/kg. The total percent uptake of the administered dose was 4.0%. Uptake into individual compartments was 2.72, 0.38, 0.15, 0.41, and 0.32% for blood, brain, heart, liver, and kidney respectively. All animals showed signs of intoxication within 20 s manifested as lethargy, prostration and loss of righting reflex. Marked intoxication continued for about 4 min when DFE averaged 21 mg/L in blood and 17 mg/kg in brain. Between 4 and 8 min, animals continued to show signs of sedation as evidenced by reduced aggression and excitement during handling. No discernable intoxication was evident after 8 min and blood and brain levels had fallen to 10 and 6 mg/L or kg, respectively. Plots of concentration (log) versus time were consistent with a two compartment model. Initial distribution was rapid with average half life (t½) during the α phase of 9 s for blood, 18 s for brain and 27 s in cardiac tissue. During β slope elimination average t½ was 86 s in blood, 110 s in brain and 168 s in heart. Late elimination half lives were longer with blood γ = 240 s, brain γ = 340 s, and heart γ = 231 s. Following acute exposure the Vd = 0.06 L, β = 0.48 min^–1, AUC = 409.8 mg · min L^–1, and CL from blood was 0.03 L min^–1. The calculated toxicokinetic data may underestimate these parameters if DFE is abused chronically due to continued uptake into lowly perfused tissues with repeated dosing.

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Journal of Analytical Toxicology: September 2010 $90.00