<prompt> HCN causes -Histotoxic anoxia by inhibiting carbonic anhydraseHistotoxic anoxia by inhibiting succinyl oxidaseCytotoxic anoxia by inhibiting cytochrome oxidaseCytotoxide anoxia by inhibiting succinyl oxidase  <response>: Hydrocyanic acid Cyanide occurs as solid, liquid or in gaseous state as: Gas form -- Hydrogen cyanide HCN Liquid form -- Hydrocyanic acid Prussic acid Solid form -- occurs as salts such as potassium cyanide sodium cyanide. Mechanism of Action Cyanide reversibly inhibits ferric iron containing enzymes. Cyanide attaches to the iron of the prosthetic group of cytochrome oxidase resulting in disturbance of the transpo and utilization of oxygen in cells and causing a cytotoxic anoxia. Fatal Dose 50 to 100 mg for hydrocyanic acid 200 to 300 mg for sodiumpotassium cyanide 50 to 80 bitter almonds Inhalation of 1 pa in 2000 -- hydrogen cyanide Fatal period: 2 to 10 minutes. Clinical Features Inhalation Constriction about throat Dizziness Loss of consciousness Coma Death Ingestion CNS: Headache, anxiety, agitation, dizziness, confusion, convulsions, coma CVS: Initially bradycardia and hypeension and latter tachycardia and hypotension, arrhythmias RS: Tachypnea followed by bradypnea GIT: Nausea, vomiting, abdominal pain, numbness. Skin Perspiration Bullae. Chronic poisoning: Chronic low level of exposure leads to: Headache Amblyopia Optic atrophy Peripheral neuropathy Ataxia Deafness Glossitis Stomatitis. Management Ingestion: gastric lavage with 5 percent sodium thiosulfate solution Antidote- amyl nitrate -- inhaled Sodium nitrate slowly I.V. Sodium thiosulfate 25 percent solution I.V. Mechanism of action of nitrites: nitrates induce methemoglobinemia, which causes detachment of cyanide from the heme group of cytochrome oxidase since methemoglobin has a higher binding affinity for cyanide. Cyanide combines with methemoglobin and form non-toxic cynmethemoglobin. Mechanism of action of sodium thiosulfate: sodium thiosulfate serves as a substrate for the enzyme rhodanese to catabolise cyanide to non-toxic thiocyanate, which is excreted in the urine. Autopsy Findings Bitter almond like smell Cherry red color of postmoem lividity Cyanosis Froth at mouth and nose Bright red color blood9 Pulmonary edema Serosal surface may show hemorrhages Stomach mucosa may be eroded and blackened due to formation of alkaline hematin. Samples to be preserved for chemical analysis Blood Routine viscera Lung Brain Hea Spleen is considered as best specimen due to presence of more RBCs. REF;THE SYNOPSIS OF FORENSIC MEDICINE:KS NARAYANA REDDY;28th EDITION;PAGE NO 362 