Methemoglobinemia, nitrites causing

Amyl nitrite causes methemoglobinemia, unconsciousness, dizziness, fatigue, shortness of breath, nausea, and vomiting. The skin is initially warm and sweaty and later becomes cold due to vasodilation. It causes coronary blood vessel contraction, bradycardia, atrial fibrillation, cardiac ischemia, headache, convulsions, and diarrhea. 

Significant levels of methemoglobinemia were produced when mice were exposed to butyl nitrites via inhalation. Pretreatment of the mice with methylene blue prevented the methemoglobin formation associated with the butyl nitrite exposure. A single intravenous dose of 30 mg kg of sodium nitrite caused methemoglobinemia in dogs. The minimum lethal dose of sodium nitrite is estimated to be 150-170 mg kg in cattle and 70-75 mg kg in pigs. 

Organic nitrites Amyl nitrite, isobutyl nitrite, and other organic nitrites are referred to as poppers and are mainly used as sexual intercourse "enhancers. Inhalation of the nitrites causes dizziness, tachycardia, hypotension, and flushing. With the exception of methemoglobinemia, few serious adverse effects have been reported,... 

The gut bacteria may also reduce nitrates to nitrites, which can cause methemoglobinemia or may react with secondary amines in the acidic environment of the gut, giving rise to carcinogenic nitrosamines. 

Numerous substances detected in drinking waters are known to induce toxicity but usually at dose levels much higher than those found in water. Nitrates or nitrites can cause infant methemoglobinemia, lead can affect the hematopoetic or nervous system, cadmium can cause renal damage, and some organohalogens may cause liver toxicity (12). 

Table 7.1 presents the most important biochemical features obtained for the infants included in the study. All water samples collected from the areas known for an intense use of nitrogen mineral fertilizers exceeded the maximum contaminant level for nitrates of 50 mg Lthereby indicating that the acute nitrate/nitrite intoxication caused the clinically evaluated methemoglobinemia. 

SAFETY PROFILE A poison by ingestion and intraperitoneal routes. Mildly toxic by inhalation. An irritant. Human systemic effects by ingestion methemoglobinemia-carboxyhemoglobinemia. Resembles amyl nitrite in causing fall in blood pressure, headache, pulse throbbing, and weakness. Mutation data reported. Flammable when exposed to heat or flame or by spontaneous chemical reaction. When heated to decomposition it emits toxic fumes of NOx. See also NITRITES, n-BUTYL ALCOHOL, and ESTERS. 

In contrast, amyl nitrite can cause methemoglobinemia when abused, since it has a 2000 times higher affinity for hemoglobin (58). In vitro both amyl nitrite and glyceryl trinitrate reacted immediately with oxyhemoglobin to effect oxidation to methemoglobin, while for sodium nitrite there was a lag phase before the reaction occurred. The affinity rate constants were ... 

Nitrites bind to hemoglobin causing oxidation of hemoglobin to methemoglobin, which is unable to transport oxygen. When methemoglobinemia exceeds 10-15%, cyanosis may become apparent. 

Nitrite is a severe respiratory, eye, and skin irritant. Acute exposure to high levels of nitrites can be fatal. Exposure may cause visual field defects, hypotension, tachycardia, respiratory depression, and cyanosis due to formation of methemoglobinemia. Symptoms may... 

Methemoglobinemia never occurs from the doses of nitroglycerin (or other nitrates) used to treat angina. The nitrites (in large doses) cause methemoglobinemia. The answer is (D). 

Nitrites, not nitrates, cause methemoglobinemia in adults. Headache, not angina, increased upon returning to work on Monday. Neither nitrates nor nitrites are related to causation of cyanide poisoning, but nitrites are used as one part of the antidote for cyanide intoxication. The answer is (D). 

Male preteen children are most likely to experiment with solvent inhalation. Abuse of nitrous oxide is relatively common. Toxic inhalants such as heptane, hexane, methylethylketone, toluene, and trichloroethylene may result in central and peripheral neurotoxicity, liver and kidney damage, and pulmonary disease. Sudden death has occurred following inhalation of fluorocarbons. Industrial solvents rarely cause methemoglobinemia, but this (and headaches) may occur following excessive use of nitrites. The answer is (C). 

B. Specific drugs and antidotes. Theoretically, administration of nitrites (see p 476) to produce methemoglobinemia may promote conversion of sulfide ions to sulfmethemoglobin, which is far less toxic. However, there is limited evidence for the effectiveness of nitrites, and they can cause hypotension and impaired oxygen delivery. Animal data and limited human case reports have suggested that hyperbaric oxygen (HBO, see p 482) may be helpful if provided early after exposure, but this therapy remains unproven. 

Cyanide poisoning. Empiric antidotal therapy with sodium thiosulfate (see p 505) and (if available) hydroxocobalamin (p 453) is recommended for patients with altered mental status, hypotension, or acidosis. Use of sodium nitrite is discouraged because it may cause hypotension and aggravate methemoglobinemia. 

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