Sodium Nitroprusside

1 INDICATIONS AND USAGE Sodium nitroprusside is a direct acting vasodilator indicated for: •Immediate reduction of blood pressure ( 1.1 ) •Producing controlled hypotension to reduce bleeding during surgery. ( 1.2 ) •Treatment of acute heart failure to reduce left ventricular end-diastolic pressure, pulmonary capillary wedge pressure, peripheral vascular resistance and mean arterial blood pressure. ( 1.3 ) 1.1 Immediate Reduction of Blood Pressure Sodium nitroprusside is indicated for the immediate reduction of blood pressure of adult and pediatric patients in hypertensive crises. 1.2 Induction and Maintenance of Controlled Hypotension Sodium nitroprusside indicated for induction and maintenance of controlled hypotension in adults and children during surgery, to reduce bleeding. 1.3 Treatment of Acute Heart Failure Sodium nitroprusside is indicated for the treatment of acute heart failure to reduce, left ventricular end-diastolic pressure, pulmonary capillary wedge pressure, peripheral vascular resistance and mean arterial blood pressure.

DOSAGE AND ADMINISTRATION Dilution to proper strength for infusion: Depending on the desired concentration, the solution containing 50 mg of sodium nitroprusside must be further diluted in 250 to 1000 mL of sterile 5% dextrose injection. The diluted solution should be protected from light, using the supplied opaque sleeve, aluminum foil, or other opaque material. It is not necessary to cover the infusion drip chamber or the tubing. Verification of the chemical integrity of the product: Sodium nitroprusside solution can be inactivated by reactions with trace contaminants. The products of these reactions are often blue, green, or red, much brighter than the faint brownish color of unreacted sodium nitroprusside injection. Discolored solutions, or solutions in which particulate matter is visible, should not be used. If properly protected from light, the freshly diluted solution is stable for 24 hours. No other drugs should be administered in the same solution with sodium nitroprusside. Avoidance of excessive hypotension: While the average effective rate in adult and pediatric patients is about 3 mcg/kg/min, some patients will become dangerously hypotensive when they receive sodium nitroprusside at this rate. Infusion of sodium nitroprusside should therefore be started at a very low rate (0.3 mcg/kg/min), with upward titration every few minutes until the desired effect is achieved or the maximum recommended infusion rate (10 mcg/kg/min) has been reached. Because sodium nitroprusside’s hypotensive effect is very rapid in onset and in dissipation, small variations in infusion rate can lead to wide, undesirable variations in blood pressure. Since there is inherent variation in blood pressure measurement, confirm the drug effect at any infusion rate after an additional 5 minutes before titrating to a higher dose to achieve the desired blood pressure. Sodium nitroprusside should not be infused through ordinary I.V. apparatus, regulated only by gravity and mechanical clamps. Only an infusion pump, preferably a volumetric pump, should be used. Because sodium nitroprusside can induce essentially unlimited blood-pressure reduction, the blood pressure of a patient receiving this drug must be continuously monitored , using either a continually reinflated sphygmomanometer or (preferably) an intra-arterial pressure sensor. Special caution should be used in elderly patients, since they may be more sensitive to the hypotensive effects of the drug. When sodium nitroprusside is used in the treatment of acute congestive heart failure, titration of the infusion rate must be guided by the results of invasive hemodynamic monitoring with simultaneous monitoring of urine output. Sodium nitroprusside can be titrated by increasing the infusion rate until: • measured cardiac output is no longer increasing, • systemic blood pressure cannot be further reduced without compromising the perfusion of vital organs, or • the maximum recommended infusion rate has been reached, whichever comes earliest. Specific hemodynamic goals must be tailored to the clinical situation, but improvements in cardiac output and left ventricular filling pressure must not be purchased at the price of undue hypotension and consequent hypoperfusion. Table 2 below shows the infusion rates corresponding to the recommended initial and maximal doses (0.3 mcg/kg/min and 10 mcg/kg/min, respectively) for both adult and pediatric patients of various weights. This infusion rate may be lower than indicated in the table for patients less than 10 kg. Note that when the concentration used in a given patient is changed, the tubing is still filled with a solution at the previous concentration. Table 2: Infusion Rates (mL/hour) to Achieve Initial (0.3 mcg/kg/min) and Maximal (10 mcg/kg/min) Dosing of Sodium Nitroprusside Volume Sodium Nitroprusside concentration 250 mL 50 mg 200 mcg/mL 500 mL 50 mg 100 mcg /mL 1000 mL 50 mg 50 mcg /mL pt kg weight lbs init max init max init max 10 22 1 30 2 60 4 120 20 …

3 DOSAGE FORMS AND STRENGTHS Injection: 50 mg/100 mL of 0.9% sodium chloride (0.5 mg/mL), 20 mg/100 mL of 0.9% sodium chloride (0.2 mg/mL), and 10 mg/50 mL of 0.9% sodium chloride (0.2 mg/mL). Sodium Nitroprusside in 0.9% Sodium Chloride Injection, ready to use is supplied as a sterile, unpreserved, colorless to red-brown solution available in a single-dose vial. Injection: 50 mg of sodium nitroprusside in 100 mL of 0.9% sodium chloride (0.5 mg/mL) in 100 mL single-dose vials, 20 mg of sodium nitroprusside in 100 mL of 0.9% sodium chloride (0.2 mg/mL) in 100 mL single-dose vials and 10 mg of sodium nitroprusside in 50 mL of 0.9% sodium chloride (0.2 mg/mL) in 50 mL single-dose vials ( 3 ).

CONTRAINDICATIONS Sodium nitroprusside should not be used in the treatment of compensatory hypertension, where the primary hemodynamic lesion is aortic coarctation or arteriovenous shunting. Sodium nitroprusside should not be used to produce hypotension during surgery in patients with known inadequate cerebral circulation, or in moribund patients (A.S.A. Class 5E) coming to emergency surgery. Patients with congenital (Leber's) optic atrophy or with tobacco amblyopia have unusually high cyanide/thiocyanate ratios. These rare conditions are probably associated with defective or absent rhodanase, and sodium nitroprusside should be avoided in these patients. Sodium nitroprusside should not be used for the treatment of acute congestive heart failure associated with reduced peripheral vascular resistance such as high-output heart failure that may be seen in endotoxic sepsis.

ADVERSE REACTIONS The most important adverse reactions to sodium nitroprusside are the avoidable ones of excessive hypotension and cyanide toxicity, described above under WARNINGS . The adverse reactions described in this section develop less rapidly and, as it happens, less commonly. Methemoglobinemia: As described in CLINICAL PHARMACOLOGY above, sodium nitroprusside infusions can cause sequestration of hemoglobin as methemoglobin. The back-conversion process is normally rapid, and clinically significant methemoglobinemia (>10%) is seen only rarely in patients receiving Sodium nitroprusside injection. Even patients congenitally incapable of back-converting methemoglobin should demonstrate 10% methemoglobinemia only after they have received about 10 mg/kg of sodium nitroprusside, and a patient receiving sodium nitroprusside at the maximum recommended rate (10 mcg/kg/min) would take over 16 hours to reach this total accumulated dose. Methemoglobin levels can be measured by most clinical laboratories. The diagnosis should be suspected in patients who have received >10 mg/kg of sodium nitroprusside and who exhibit signs of impaired oxygen delivery despite adequate cardiac output and adequate arterial pO 2 . Classically, methemoglobinemic blood is described as chocolate brown, without color change on exposure to air. When methemoglobinemia is diagnosed, the treatment of choice is 1-2 mg/kg of methylene blue, administered intravenously over several minutes. In patients likely to have substantial amounts of cyanide bound to methemoglobin as cyanmethemoglobin, treatment of methemoglobinemia with methylene blue must be undertaken with extreme caution. Thiocyanate Toxicity: As described in CLINICAL PHARMACOLOGY above, most of the cyanide produced during metabolism of sodium nitroprusside is eliminated in the form of thiocyanate. When cyanide elimination is accelerated by the co-infusion of thiosulfate, thiocyanate production is increased. Thiocyanate is mildly neurotoxic (tinnitus, miosis, hyperreflexia) at serum levels of 1 mmol/L (60 mg/L). Thiocyanate toxicity is life-threatening when levels are 3 or 4 times higher (200 mg/L). The steady-state thiocyanate level after prolonged infusions of sodium nitroprusside is increased with increased infusion rate, and the half-time of accumulation is 3-4 days. To keep the steady-state thiocyanate level below 1 mmol/L, a prolonged infusion of sodium nitroprusside should not be more rapid than 3 mcg/kg/min; in anuric patients, the corresponding limit is just 1 mcg/kg/min. When prolonged infusions are more rapid than these, thiocyanate levels should be measured daily. Physiologic maneuvers (e.g., those that alter the pH of the urine) are not known to increase the elimination of thiocyanate. Thiocyanate clearance rates during dialysis, on the other hand, can approach the blood flow rate of the dialyzer. Thiocyanate interferes with iodine uptake by the thyroid. Abdominal pain, apprehension, diaphoresis, “dizziness,” headache, muscle twitching, nausea, palpitations, restlessness, retching, and retrosternal discomfort have been noted when the blood pressure was too rapidly reduced. These symptoms quickly disappeared when the infusion was slowed or discontinued, and they did not reappear with a continued (or resumed) slower infusion. Other adverse reactions reported are: Cardiovascular: Bradycardia, electrocardiographic changes, tachycardia. Dermatologic: Rash. Endocrine: Hypothyroidism. Gastrointestinal: Ileus. Hematologic: Decreased platelet aggregation. Neurologic: Increased intracranial pressure. Miscellaneous: Flushing, venous streaking, irritation at the infusion site. To report SUSPECTED ADVERSE REACTIONS, contact Meitheal Pharmaceuticals Inc. at 1-844-824-8426 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.

Drug Interactions: The hypotensive effect of sodium nitroprusside is augmented by that of most other hypotensive drugs, including ganglionic blocking agents, negative inotropic agents, and inhaled anesthetics.

8 USE IN SPECIFIC POPULATIONS 8.1 Pregnancy Risk Summary Based on animal data and mechanism of action, sodium nitroprusside may lead to cyanide exposure and potential adverse effects in the fetus [see Clinical Pharmacology ( 12.3 ) and Clinical Considerations] . Published post-marketing reports with sodium nitroprusside use in pregnant women are insufficient to inform a drug-associated risk of adverse pregnancy related outcomes [see Data] . There were no animal reproduction studies conducted with sodium nitroprusside during pregnancy. However, there are published studies in pregnant sheep that demonstrate that nitroprusside crosses the placenta and that fetal cyanide levels were dose-related to maternal levels of sodium nitroprusside [see Data]. Advise pregnant women of the potential risk to a fetus. The estimated background risk of major birth defects and miscarriage for the indicated population is unknown. All pregnancies have a background risk of birth defect, loss, or other adverse outcomes. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2-4% and 15-20%, respectively. Clinical Considerations Fetal/Neonatal Adverse Reactions Prolonged use and large doses of sodium nitroprusside during pregnancy may result in cyanide toxicity that may be fatal to the fetus. In the unusual case that there is no appropriate alternative to therapy with sodium nitroprusside for a particular patient, apprise the mother of the potential risk to the fetus [see Warnings and Precautions ( 5.2 )] . Data Human Data A small number of cases have reported adverse events, including stillbirths, in pregnant women with severe pregnancy-induced hypertension who were treated with sodium nitroprusside. However, methodological limitations, including small sample size and limited information on sodium nitroprusside dosage and duration of treatment, as well as the cyanide concentration in maternal blood or fetal tissue, preclude a reliable evaluation of the potential risk of adverse fetal outcomes with the use of sodium nitroprusside during pregnancy. Animal Data In three studies in pregnant ewes, nitroprusside was shown to cross the placental barrier. Fetal cyanide levels were shown to be dose-related to maternal levels of nitroprusside. The metabolic transformation of sodium nitroprusside given to pregnant ewes led to fatal levels of cyanide in the fetuses. The infusion of 25 mcg/kg/min of sodium nitroprusside for one hour in pregnant ewes resulted in the death of all fetuses. Pregnant ewes infused with 1 mcg/kg/min of sodium nitroprusside for one hour delivered normal lambs. 8.2 Lactation Risk Summary There is no information about the presence of sodium nitroprusside in human milk, the effects on the breastfed infant, or the effects on milk production. Thiocyanate, one of sodium nitroprusside’s metabolites, is present in human milk. It is unclear how long, if ever, levels of thiocyanate in milk are clinically relevant. 8.4 Pediatric Use Efficacy in the pediatric population was established based on adult trials and supported by the dose-ranging trial (Study 1) and an open label trial of at least 12 hour infusion at a rate that achieved adequate MAP control (Study 2) with pediatric patients on sodium nitroprusside. No novel safety issues were seen in these studies in pediatric patients [see Clinical Studies ( 14 )].

11 DESCRIPTION Sodium nitroprusside is disodium pentacyanonitrosylferrate(2-) dihydrate, a hypotensive agent whose structural formula is Sodium Nitroprusside has molecular formula Na 2 [Fe(CN) 5 NO] • 2H 2 O and molecular weight of 297.95. Dry sodium nitroprusside is a reddish-brown powder, soluble in water. Sodium nitroprusside solution is rapidly degraded by trace contaminants, often with resulting color changes [see Dosage and Administration ( 2.1 )] . Sodium Nitroprusside in 0.9% Sodium Chloride Injection, ready to use is supplied as a sterile, unpreserved, colorless to red-brown solution packaged in a single-dose 100-mL vial. Each 100 mL of solution in vial contains 50 mg of sodium nitroprusside (0.5 mg/mL), 900 mg of sodium chloride, USP (9 mg/mL), in sterile water for injection, USP. Sodium Nitroprusside in 0.9% Sodium Chloride Injection, ready to use is also supplied as a sterile, unpreserved, colorless to red-brown solution packaged in a single-dose 100-mL vial. Each 100 mL of solution in vial contains 20 mg of sodium nitroprusside (0.2 mg/mL), 900 mg of sodium chloride, USP (9 mg/mL), in sterile water for injection, USP. Sodium Nitroprusside in 0.9% Sodium Chloride Injection, ready to use is also supplied as a sterile, unpreserved, colorless to red-brown solution packaged in a single-dose 50-mL vial. Each 50 mL of solution in vial contains 10 mg of sodium nitroprusside (0.2 mg/mL), 450 mg of sodium chloride, USP (9 mg/mL), in sterile water for injection, USP. structure

OVERDOSAGE Overdosage of nitroprusside can be manifested as excessive hypotension or cyanide toxicity (see WARNINGS ) or as thiocyanate toxicity (see ADVERSE REACTIONS ). The acute intravenous mean lethal doses (LD50) of nitroprusside in rabbits, dogs, mice, and rats are 2.8, 5.0, 8.4, and 11.2 mg/kg, respectively. Treatment of cyanide toxicity: Cyanide levels can be measured by many laboratories, and blood-gas studies that can detect venous hyperoxemia or acidosis are widely available. Acidosis may not appear until more than an hour after the appearance of dangerous cyanide levels, and laboratory tests should not be awaited. Reasonable suspicion of cyanide toxicity is adequate grounds for initiation of treatment. Treatment of cyanide toxicity consists of • discontinuing the administration of sodium nitroprusside; • providing a buffer for cyanide by using sodium nitrite to convert as much hemoglobin into methemoglobin as the patient can safely tolerate; and then • infusing sodium thiosulfate in sufficient quantity to convert the cyanide into thiocyanate. The necessary medications for this treatment are contained in commercially available Cyanide Antidote Kits. Alternatively, discrete stocks of medications can be used. Hemodialysis is ineffective in removal of cyanide, but it will eliminate most thiocyanate. Cyanide Antidote Kits contain both amyl nitrite and sodium nitrite for induction of methemoglobinemia. The amyl nitrite is supplied in the form of inhalant ampoules, for administration in environments where intravenous administration of sodium nitrite may be delayed. In a patient who already has a patent intravenous line, use of amyl nitrite confers no benefit that is not provided by infusion of sodium nitrite. Sodium nitrite is available in a 3% solution, and 4 to 6 mg/kg (about 0.2 mL/kg) should be injected over 2 to 4 minutes. This dose can be expected to convert about 10% of the patient’s hemoglobin into methemoglobin; this level of methemoglobinemia is not associated with any important hazard of its own. The nitrite infusion may cause transient vasodilatation and hypotension, and this hypotension must, if it occurs, be routinely managed. Immediately after infusion of the sodium nitrite, sodium thiosulfate should be infused. This agent is available in 10% and 25% solutions, and the recommended dose is 150 to 200 mg/kg; a typical adult dose is 50 mL of the 25% solution. Thiosulfate treatment of an acutely cyanide-toxic patient will raise thiocyanate levels, but not to a dangerous degree. The nitrite/thiosulfate regimen may be repeated, at half the original doses, after two hours.

HOW SUPPLIED Sodium nitroprusside Injection is supplied as follows: NDC Sodium Nitroprusside Injection (25 mg per mL) Package Factor 71288- 202 -02 50 mg per 2 mL in amber-colored, single-dose Fliptop Vials 1 vial per carton STORAGE: Store at 20 to 25°C (68 to 77°F). [See USP Controlled Room Temperature.] To protect Sodium nitroprusside injection from light, it should be stored in its carton until it is used. Discard unused portion. Sterile, Nonpyrogenic, Preservative-free. The container closure is not made with natural rubber latex. meitheal ® Mfd. for Meitheal Pharmaceuticals Chicago, IL 60631 (USA) ©2020 Meitheal Pharmaceuticals Inc. January 2020 Code: TN/Drugs/TN00003457