Nitrite poisoning can occur by accidental ingestion of food and water or through recreational inhalation of amyl nitrite. Severe nausea, vomiting, fatigue, dizziness and methemoglobinemia inducing profound cyanosis are main symptoms. Rapid use of methylene blue can be life-saving, as coma and death can ensue if an early diagnosis is not made.
Because of its antiseptic properties, the ability to control oxidation of lipids, but also because it gives flavor and color to meat products, nitrites (mainly in the form of sodium nitrite) are used for various industrial and agricultural purposes . In high amounts, however, this substance can be highly toxic for humans and nitrite poisoning can occur through accidental ingestion of contaminated food and water, or through inhalation of amyl nitrite for recreational purposes  . The onset of symptoms is approximately 60 minutes and include dizziness, fatigue, nausea, vomiting and profound cyanosis . Methemoglobinemia, a condition in which hemoglobin is replaced by methemoglobin that is unable to bind oxygen, is the main cause of symptoms seen in nitrite poisoning and can lead to tachycardia, loss of consciousness and even coma  . The diagnosis can be made by obtaining a detailed personal history that can reveal the source of poisoning, but rapid and profound cyanosis without an apparent cause is highly suspective of nitrite poisoning . Immediate intravenous administration of methylene blue is the mainstay of therapy and the prognosis can be fatal in the setting of profound methemoglobinemia .
Nitrites in the form of sodium nitrite are used to preserve meat and fish products because of their antimicrobial effects, but they are also used for prevention of pipe corrosion and fertilization . They are rarely found in concentrations sufficient to cause toxicity . Recreational inhalation of amyl nitrite and accidental ingestion of sodium nitrite (resembling sugar and salt) are recognized modes of poisoning and between 200-500 mg are sufficient to cause severe symptoms  .
Nitrite poisoning is rarely reported and data regarding this condition are frequently extracted from isolated reports, but the majority of cases come from China, where sodium nitrite can be easily purchased and is frequently mistaken as salt or sugar due to similar appearance .
The toxic effects of nitrites in the human body are exerted by its potent conversion of oxyhemoglobin to methemoglobin, which leads to profound cyanosis and reduced oxygen saturation of tissues. The presumed mechanism is thought to be an oxido-reductive reaction that produces NO2 and renders hemoglobin unable to bind oxygen . As a result, the newly converted methemoglobin is the primary cause of numerous symptoms seen in these patients .
Poisoning by nitrites can be fatal in high concentrations and without appropriate therapy . For this reason, early recognition of the disease is detrimental.
Symptoms of nitrite poisoning start within a range of 20-180 minutes, most prominent being nausea, vomiting, dizziness and fatigue . Marked cyanosis caused by methemoglobinemia manifests on the lips, fingernails and skin, followed by tachycardia and loss of consciousness . As the percentage of methemoglobin rises, further deterioration of clinical signs and symptoms are seen and can lead to coma and death .
Cyanosis that does not improve on supplemental oxygen is highly suggestive of methemoglobinemia induced by nitrites . Because oxygen saturation is not a reliable diagnostic sign, one of the most prominent clinical signs is the appearance of "chocolate brown" blood when drawing samples for testing  . The diagnosis mandates a detailed patient history and evaluation of family members, as clustered cases of accidental ingestion are the most common clinical setting  .
Immediate administration of 1% methylene blue is recommended, as it is able to reverse the effects of nitrite-induced methemoglobinemia . It is given intravenously in doses of 1-2 mg/kg .
Although sodium nitrite is rarely found in household items, its availability on the market in countries like China presents as a significant risk for poisoning . Avoiding recreational use of amyl nitrite may also be an important preventive strategy, as poisoning after inhalation has been reported .
Nitrites are compounds used for preservation of certain food products, such as meat and fish, primarily because of their antimicrobial properties. They are rarely found in concentrations high enough to cause toxicity, but accidental ingestion of water or food containing very high amounts of this inorganic substance is the most frequent mode of poisoning. Namely, nitrites induce conversion of hemoglobin to methemoglobin, which is unable to bind oxygen, resulting in the appearance of severe and life-threatening symptoms. Nausea, vomiting, dizziness and extreme fatigue develop within three hours after nitrites are introduced into the body, followed by the onset of profound cyanosis - marked bluish-to-purple discoloration of lips, fingers and nails due to absence of oxygen. In severe cases, lack of oxygen in tissues can cause coma and even death. For this reason, prompt recognition of the disease is mandatory. Nitrite poisoning is distinguished by the appearance of cyanosis that is not improving after supplementation with oxygen and by observing a brown to chocolate color of blood when drawing samples for testing. Treatment includes immediate intravenous administration of methylene blue, which enables conversion of methemoglobin back to hemoglobin.