Sodium Nitrite and Sodium Thiosulfate

NITHIODOTE is indicated for the treatment of acute cyanide poisoning that is judged to be serious or life-threatening. When the diagnosis of cyanide poisoning is uncertain, carefully weigh the potentially life-threatening risks associated with NITHIODOTE against the potential benefits, especially if the patient is not in extremis. NITHIODOTE, an antidote, is indicated for the treatment of acute cyanide poisoning that is judged to be serious or life-threatening. ( 1 ) Use with caution if the diagnosis of cyanide poisoning is uncertain. ( 1 )

NITHIODOTE Injection consists of: One vial of sodium nitrite injection, USP 300 mg/10 mL (30 mg/mL) and One vial of sodium thiosulfate injection USP 12.5 grams/50 mL (250 mg/mL) Administration of one vial of each medication constitutes a single dose. NITHIODOTE consists of: one vial of sodium nitrite injection, USP 300 mg/10 mL (30 mg/mL) and one vial of sodium thiosulfate injection, USP 12.5 grams/50 mL (250 mg/mL). ( 3 )

None None. ( 4 )

Methemoglobinemia: Sodium nitrite reacts with hemoglobin to form methemoglobin and should be used with caution in patients known to have anemia. Monitor oxyhemoglobin and methemoglobin levels by pulse co-oximetry or other measurements. Optimally, the sodium nitrite dose should be reduced in proportion to the oxygen carrying capacity. ( 5.2 ) Smoke inhalation: Carbon monoxide contained in smoke can result in the formation of carboxyhemoglobin that can reduce the oxygen carrying capacity of the blood. Sodium nitrite should be used with caution in patients with smoke inhalation injury because of the potential for worsening hypoxia due to methemoglobin formation. Carboxyhemoglobin and oxyhemoglobin levels should be monitored by pulse oximetry or other measurements in patients that present with evidence of smoke inhalation. Optimally, the sodium nitrite dose should be reduced in proportion to the oxygen carrying capacity. ( 5.4 )

5.1 Hypotension Sodium nitrite has been associated with severe hypotension, methemoglobinemia, and death at doses less than twice recommended therapeutic doses. Hypotension may occur concurrently or separately. Sodium nitrite should be used to treat life-threatening cyanide poisoning. When the diagnosis of cyanide poisoning is uncertain and/or the patient is not in extremis, special consideration should be given to administration of sodium nitrite if the patient is known or suspected to have diminished oxygen or cardiovascular reserve (e.g., smoke inhalation victims, pre-existing anemia, substantial blood loss, cardiac or respiratory compromise) or to be at higher risk of developing methemoglobinemia (e.g., congenital methemoglobin reductase deficiency).

5.2 Methemoglobinemia Supportive care alone may be sufficient treatment without administration of antidotes for many cases of cyanide intoxication, particularly in conscious patients without signs of severe toxicity. Monitor patients closely to ensure adequate perfusion and oxygenation during treatment with sodium nitrite. Monitor methemoglobin levels and administer oxygen during treatment with sodium nitrite whenever possible. When sodium nitrite is administered to humans a wide range of methemoglobin concentrations occur. Methemoglobin concentrations as high as 58% have been reported after two 300-mg doses of sodium nitrite administered to an adult. Sodium nitrite should be used with caution in the presence of other drugs that may cause methemoglobinemia such as procaine and nitroprusside. Use sodium nitrite with caution in patients who may be particularly susceptible to injury from vasodilation and its related hemodynamic sequelae. Monitor hemodynamics closely during and after administration of sodium nitrite and sodium thiosulfate, and reduce infusion rates if hypotension occurs.

5.3 Anemia Use sodium nitrite with caution in patients with known anemia. Patients with anemia will form more methemoglobin (as a percentage of total hemoglobin) than persons with normal red blood cell (RBC) volumes. Optimally, these patients should receive a sodium nitrite dose that is reduced in proportion to their oxygen carrying capacity.

5.4 Smoke Inhalation Injury Use sodium nitrite with caution in persons with smoke inhalation injury or carbon monoxide poisoning because of the potential for worsening hypoxia due to methemoglobin formation.

5.5 Neonates and Infants Neonates and infants may be more susceptible than adults and older pediatric patients to severe methemoglobinemia when sodium nitrite is administered. Follow reduced dosing guidelines in pediatric patients. 5.6 G6PD Deficiency Because patients with G6PD deficiency are at increased risk of a hemolytic crisis with sodium nitrite administration, consider alternative therapeutic approaches in these patients. Monitor patients with known or suspected G6PD deficiency for an acute drop in hematocrit. Exchange transfusion may be needed for patients with G6PD deficiency who receive sodium nitrite.

5.7 Use with Other Drugs Use sodium nitrite with caution in the presence of concomitant antihypertensive medications, diuretics or volume depletion due to diuretics, or drugs known to increase vascular nitric oxide, such as PDE5 inhibitors.

5.8 Sulfites Sodium thiosulfate drug product may contain trace impurities of sodium sulfite. The presence of a trace amount of sulfites in this product should not deter administration of the drug for treatment of emergency situations, even if the patient is sulfite-sensitive.

There have been no controlled clinical trials conducted to systematically assess the adverse events profile of sodium nitrite or sodium thiosulfate. The medical literature has reported the following adverse events in association with sodium nitrite or sodium thiosulfate administration. These adverse events were not reported in the context of controlled trials or with consistent monitoring and reporting methodologies for adverse events. Therefore, frequency of occurrence of these adverse events cannot be assessed. Most common adverse reactions are: Sodium nitrite : syncope, hypotension, tachycardia, palpitations, dysrhythmia, methemoglobinemia, headache, dizziness, blurred vision, seizures, confusion, coma ( 6 ) Sodium thiosulfate : hypotension, headache, disorientation ( 6 ) To report SUSPECTED ADVERSE REACTIONS, contact Hope Pharmaceuticals at 1-800-755-9595 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch . S odium Nitrite Cardiovascular system: syncope, hypotension, tachycardia, methemoglobinemia, palpitations, dysrhythmia Hematological: methemoglobinemia Central nervous system: headache, dizziness, blurred vision, seizures, confusion, coma Gastrointestinal system: nausea, vomiting, abdominal pain Respiratory system: tachypnea, dyspnea Body as a Whole : anxiety, diaphoresis, lightheadedness, injection site tingling, cyanosis, acidosis, fatigue, weakness, urticaria, generalized numbness and tingling Severe hypotension, methemoglobinemia, cardiac dysrhythmias, coma and death have been reported in patients without life-threatening cyanide poisoning but who were treated with injection of sodium nitrite at doses less than twice those recommended for the treatment of cyanide poisoning. Sodium Thiosulfate Cardiovascular system: hypotension Central nervous system: headache, disorientation Gastrointestinal system: nausea, vomiting Hematological : prolonged bleeding time Body as a Whole: salty taste in mouth, warm sensation over body In humans, rapid administration of concentrated solutions or solutions not freshly prepared, and administration of large doses of sodium thiosulfate have been associated with a higher incidence of nausea and vomiting. However, administration of 0.1 g sodium thiosulfate per pound up to a maximum of 15 g in a 10-15% solution over 10-15 minutes was associated with nausea and vomiting in 7 of 26 patients without concomitant cyanide intoxication. In a series of 11 human subjects, a single intravenous infusion of 50 mL of 50% sodium thiosulfate was associated with increases in clotting time 1-3 days after administration. However, no significant changes were observed in other hematological parameters.

Formal drug interaction studies have not been conducted with NITHIODOTE.

Lactation: Breastfeeding not recommended. ( 8.2 ) Renal impairment: Sodium nitrite and sodium thiosulfate are substantially excreted by the kidney. The risk of toxic reactions to these drugs may be greater in patients with impaired renal function. ( 8.6 ).

8.1 Pregnancy Risk Summary Life-sustaining therapy should not be withheld. Cyanide poisoning is a medical emergency in pregnancy, which can be fatal for the pregnant woman and fetus if left untreated (see Clinical Considerations ). Therefore, if a pregnant woman has known or suspected cyanide poisoning, Sodium Nitrite Injection for sequential use with Sodium Thiosulfate Injection is recommended [see Indications and Usage (1) ]. There are no available data on NITHIODOTE use in pregnant women to establish a drug-associated risk for major birth defects, miscarriage, or adverse maternal or fetal outcomes. If available, consider alternative therapies not associated with methemoglobinemia. There are no intravenous animal studies to evaluate the effect of sodium nitrite, sodium thiosulfate, or the combination on embryofetal development. In published animal studies, fetal mortality was reported when pregnant guinea pigs were subcutaneously administered sodium nitrite at 1.7 times the maximum recommended human dose (MRHD) of 450 mg sodium nitrite when maternal and fetal methemoglobin concentrations were at their peak. In other published studies, no evidence of malformations were reported in guinea pigs, mice, or rats; however, severe anemia, reduced growth, and increased pup mortality was reported when pregnant rats were treated with 4.7 times the MRHD of sodium nitrite via drinking water during gestation and throughout lactation. In published animal studies, no evidence of embryotoxicity or malformations was reported when sodium thiosulfate was administered orally during organogenesis to pregnant mice, rats, hamsters, or rabbits at 0.2 to 0.9 times the human daily dose of 12.5 g for cyanide poisoning. The sodium thiosulfate studies did not test doses that were comparable to the human dose for cyanide poisoning (see Data ). Clinical Considerations Disease-associated maternal and/or embryo/fetal risk Cyanide readily crosses the placenta. Cyanide poisoning is a medical emergency in pregnancy, which can be fatal for the pregnant woman and fetus if left untreated. Treatment for cyanide poisoning should not be withheld because of potential concerns regarding the effects of Nithiodote on the fetus. Fetal/neonatal adverse reactions Sodium nitrite produces methemoglobin. Fetal hemoglobin is oxidized to methemoglobin more easily than adult hemoglobin. In addition, the fetus has lower levels of methemoglobin reductase than adults [see Use in Specific Populations (8.4) ] . Based on animal studies, prenatal exposure to sodium nitrite resulted in impaired neural development likely the result of prenatal hypoxia (see Data ). If available, consider alternative therapy not known to be associated with methemoglobinemia. Data Animal Data Sodium nitrite There are no intravenous toxicology studies of sodium nitrite that evaluate the potential for reproductive and developmental toxicity. In a published study, sodium nitrite treatment of pregnant guinea pigs with 60 or 70 mg/kg/day resulted in abortion of the litters within 1-4 days of treatment. All animals treated subcutaneously with 70 mg/kg, sodium nitrite died within 60 minutes of treatment. Further studies demonstrated that a dose of 60 mg/kg resulted in measurable blood levels of methemoglobin in the dams and their fetuses for up to 6 hours post treatment. Maternal methemoglobin levels were higher than the levels in the offspring at all times measured. Based on a body surface area comparison, a 60 mg/kg dose in the guinea pig that resulted in death was only 1.7 times higher than the highest clinical dose of sodium nitrite that would be used to treat cyanide poisoning (based on a body surface area comparison). In a published study, treatment of pregnant rats via drinking water with sodium nitrite at concentrations of either 2000 or 3000 mg/L during gestation and throughout lactation resulted in severe anemia, reduced growth, and increased mortality in the offspring. This exposure regimen in the rat model would result in dosing of approximately 220 and 300 mg/kg/day (4.7 and 6.5 times the highest clinical dose of sodium nitrite that would be used to treat cyanide poisoning, based on a body surface area comparison). In a published study, treatment of pregnant mice with approximately 243 mg/kg sodium nitrite daily (2.6 times the maximum recommended daily dose of 450 mg/day based on body surface are) via the drinking water (1000 mg/L) from Gestation Day 7-18 did not result in evidence of malformations or embryofetal toxicity or maternal toxicity. Behavioral and neurodevelopmental studies in rats suggest persistent effects of prenatal exposure to sodium nitrite that were detectable postnatally. Specifically, animals that were exposed prenatally to sodium nitrite (2000 mg/L via drinking water) demonstrated impaired discrimination learning behavior (both auditory and visual) and reduced long-term retention of the passive-avoidance response compared to control animals. Additional studies demonstrated a delay in the development of AchE and 5-HT positive fiber ingrowth into the hippocampal dentate gyrus and parietal neocortex during the first week of life of prenatal nitrite treated pups. These changes have been attributed to prenatal hypoxia following nitrite exposure. Sodium thiosulfate No malformations or evidence of embryo-fetal toxicity were noted when pregnant mice, rats, hamsters, or rabbits were administered oral doses of sodium thiosulfate of up to 550, 400, 400, or 580 mg/kg, respectively during organogenesis (0.2, 0.3, 0.26, and 0.9 times the human dose of 12.5 g/60 kg person for cyanide poisoning based on body surface area). Published studies suggest that treatment with sodium thiosulfate ameliorates the teratogenic effects of maternal cyanide poisoning in hamsters.

8.2 Lactation Risk Summary There are no data on the presence of sodium nitrite or sodium thiosulfate in human or animal milk, the effects on the breastfed infant, or the effects on milk production. Cyanide and thiocyanate (which is formed when sodium thiosulfate combines with cyanide) are present in human milk. Because of the potential for serious adverse reactions in the breastfed infant, breastfeeding is not recommended during treatment with NITHIODOTE. There are no data to determine when breastfeeding may be safely restarted following the administration of NITHIODOTE.

8.4 Pediatric Use There are case reports in the medical literature of sodium nitrite in conjunction with sodium thiosulfate being administered to pediatric patients with cyanide poisoning; however, there have been no clinical studies to evaluate the safety or efficacy of sodium thiosulfate or sodium nitrite in the pediatric population. As for adult patients, dosing recommendations for pediatric patients have been based on theoretical calculations of antidote detoxifying potential, extrapolation from animal experiments, and a small number of human case reports. Use Sodium nitrite with caution in patients less than 6 months of age because they may be at higher risk of developing severe methemoglobinemia compared to older children and adults. The presence of fetal hemoglobin, which is oxidized to methemoglobin more easily than adult hemoglobin, and lower methemoglobin reductase levels compared to older children and adults may contribute to risk. Mortality attributed to sodium nitrite was reported following administration of an adult dose (300 mg IV followed by a second dose of 150 mg) to a 17-month old child. […]

Cyanide is an extremely toxic poison. In the absence of rapid and adequate treatment, exposure to a high dose of cyanide can result in death within minutes due to the inhibition of cytochrome oxidase resulting in arrest of cellular respiration. Specifically, cyanide binds rapidly with cytochrome a3, a component of the cytochrome c oxidase complex in mitochondria. Inhibition of cytochrome a3 prevents the cell from using oxygen and forces anaerobic metabolism, resulting in lactate production, cellular hypoxia and metabolic acidosis. In massive acute cyanide poisoning, the mechanism of toxicity may involve other enzyme systems as well. Signs and symptoms of acute systemic cyanide poisoning may develop rapidly within minutes, depending on the route and extent of cyanide exposure. The synergy resulting from treatment of cyanide poisoning with the combination of sodium nitrite and sodium thiosulfate is the result of differences in their primary mechanisms of action as antidotes for cyanide poisoning. Sodium Nitrite Sodium nitrite is thought to exert its therapeutic effect by reacting with hemoglobin to form methemoglobin, an oxidized form of hemoglobin incapable of oxygen transport but with high affinity for cyanide. Cyanide preferentially binds to methemoglobin over cytochrome a 3 , forming the nontoxic cyanomethemoglobin. Methemoglobin displaces cyanide from cytochrome oxidase, allowing resumption of aerobic metabolism. The chemical reaction is as follows: NaNO 2 + Hemoglobin → Methemoglobin HCN + Methemoglobin → Cyanomethemoglobin Vasodilation has also been cited to account for at least part of the therapeutic effect of sodium nitrite. It has been suggested that sodium nitrite-induced methemoglobinemia may be more efficacious against cyanide poisoning than comparable levels of methemoglobinemia induced by other oxidants. Also, sodium nitrite appears to retain some efficacy even when the formation of methemoglobin is inhibited by methylene blue. Sodium Thiosulfate The primary route of endogenous cyanide detoxification is by enzymatic transulfuration to thiocyanate (SCN – ), which is relatively nontoxic and readily excreted in the urine. Sodium thiosulfate is thought to serve as a sulfur donor in the reaction catalyzed by the enzyme rhodanese, thus enhancing the endogenous detoxification of cyanide in the following chemical reaction: Rhodanese Na 2 S 2 O 3 + CN – → SCN – + Na 2 SO 3 .