Poison & Antidote: Sodium nitrite MCQs With Answer

Introduction: Sodium nitrite is a common oxidizing agent that causes methemoglobinemia, an important topic in toxicology and clinical pharmacy. This concise, student-focused overview explains key concepts—mechanism of toxicity, clinical features, laboratory diagnosis, preventive measures, and the principal antidote, methylene blue—relevant to B.Pharm students preparing for exams and clinical practice. Emphasis on pathophysiology, detection methods, differential diagnosis and antidote precautions equips students with practical toxicology knowledge. Keywords: sodium nitrite, poison, antidote, methemoglobinemia, methylene blue, toxicology, B.Pharm, MCQs. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the primary toxic effect of sodium nitrite on hemoglobin?

• Oxidation of ferrous iron (Fe2+) to ferric iron (Fe3+) forming methemoglobin
• Chelation of iron ions removing them from hemoglobin
• Cleavage of heme ring causing hemolysis
• Irreversible binding to oxygen preventing release

Correct Answer: Oxidation of ferrous iron (Fe2+) to ferric iron (Fe3+) forming methemoglobin

Q2. Which laboratory method is most reliable to quantify methemoglobin?

• Pulse oximetry
• Co-oximetry (multi-wavelength spectrophotometry)
• Standard arterial blood gas (PaO2 only)
• Urine dipstick test

Correct Answer: Co-oximetry (multi-wavelength spectrophotometry)

Q3. A classic visual sign of significant methemoglobinemia is:

• Bright cherry-red blood
• Chocolate-brown colored blood
• Frothy pink sputum
• Dark black coagulated blood

Correct Answer: Chocolate-brown colored blood

Q4. Why can pulse oximetry be misleading in methemoglobinemia?

• Pulse oximeters measure only PaO2 not hemoglobin saturation
• Methemoglobin falsely alters absorbance leading to unreliable saturation readings
• Pulse oximetry gives exact methemoglobin fraction
• Pulse oximeters overestimate arterial oxygen tension

Correct Answer: Methemoglobin falsely alters absorbance leading to unreliable saturation readings

Q5. First-line pharmacologic antidote for symptomatic sodium nitrite–induced methemoglobinemia is:

• Ascorbic acid only
• Methylene blue
• Sodium thiosulfate
• Deferoxamine

Correct Answer: Methylene blue

Q6. The therapeutic action of methylene blue in methemoglobinemia is mainly via:

• Direct oxygen donation to tissues
• Increasing erythropoiesis to replace dysfunctional red cells
• Acting as an electron acceptor in an NADPH-dependent pathway to reduce methemoglobin
• Inhibiting nitrite absorption from the gut

Correct Answer: Acting as an electron acceptor in an NADPH-dependent pathway to reduce methemoglobin

Q7. Which congenital enzyme deficiency predisposes to chronic methemoglobinemia?

• Glucose-6-phosphate dehydrogenase (G6PD) deficiency
• Cytochrome b5 reductase (methemoglobin reductase) deficiency
• Pyruvate kinase deficiency
• Acetylcholinesterase deficiency

Correct Answer: Cytochrome b5 reductase (methemoglobin reductase) deficiency

Q8. A major clinical feature of methemoglobinemia is tissue hypoxia despite normal PaO2. This occurs because:

• Methemoglobin increases oxygen diffusion across membranes
• Ferric hemoglobin cannot bind oxygen effectively, reducing oxygen carriage and delivery
• Oxygen is bound too tightly to hemoglobin improving saturation readings
• Carbon dioxide accumulation displaces oxygen

Correct Answer: Ferric hemoglobin cannot bind oxygen effectively, reducing oxygen carriage and delivery

Q9. Which patient population is particularly susceptible to nitrite-induced methemoglobinemia?

• Elderly with well-developed reductase systems
• Newborns and infants due to lower reductive capacity and fetal hemoglobin
• Healthy adult athletes
• Patients on long-term iron supplements only

Correct Answer: Newborns and infants due to lower reductive capacity and fetal hemoglobin

Q10. Which common source is associated with accidental sodium nitrite exposure?

• Cured meats and some food preservatives
• Tap water that has been boiled
• Pure table salt (sodium chloride)
• Whole fresh fruits

Correct Answer: Cured meats and some food preservatives

Q11. In addition to methemoglobinemia, high nitrite exposure can cause which cardiovascular effect?

• Hypertension due to arterial constriction
• Bradycardia only without blood pressure change
• Peripheral vasodilation leading to hypotension
• Increased blood viscosity causing thrombosis

Correct Answer: Peripheral vasodilation leading to hypotension

Q12. Which biochemical conversion explains how ingested nitrate may lead to methemoglobinemia?

• Nitrate is rapidly chelated and excreted unchanged
• Nitrate is reduced to nitrite by oral and gut bacteria, and nitrite oxidizes hemoglobin
• Nitrate converts to nitric oxide which binds hemoglobin tightly
• Nitrate directly binds to iron in heme without conversion

Correct Answer: Nitrate is reduced to nitrite by oral and gut bacteria, and nitrite oxidizes hemoglobin

Q13. Which of the following is a known contraindication or caution for methylene blue therapy?

• Patients with cytochrome b5 reductase deficiency who tolerate methylene blue well
• Patients with G6PD deficiency because of risk of hemolysis
• Patients on vitamin C who cannot receive methylene blue
• Pregnant patients where methylene blue is always safe

Correct Answer: Patients with G6PD deficiency because of risk of hemolysis

Q14. Which additional adverse effect is commonly associated with methylene blue administration?

• Blue-green discoloration of urine and bodily fluids
• Permanent skin tattooing
• Progressive renal failure in healthy individuals
• Marked hyperglycemia

Correct Answer: Blue-green discoloration of urine and bodily fluids

Q15. Which simple bedside action is useful in the immediate management of a suspected sodium nitrite ingestion?

• Administer activated charcoal if presentation is early and ingestion was recent
• Perform exchange transfusion as the first step without stabilization
• Give aspirin to reduce oxidation
• Encourage vomiting at all costs

Correct Answer: Administer activated charcoal if presentation is early and ingestion was recent

Q16. Which diagnostic discrepancy is characteristic of methemoglobinemia?

• High pulse oximetry with low PaO2
• Low pulse oximetry with normal arterial oxygen tension (PaO2)
• High PaO2 with high oxygen content
• Normal pulse oximetry and reduced hemoglobin concentration only

Correct Answer: Low pulse oximetry with normal arterial oxygen tension (PaO2)

Q17. Which enzyme system provides the primary physiologic reduction of methemoglobin in erythrocytes?

• NADH-dependent cytochrome b5 reductase system
• Glutathione peroxidase only
• Catalase-mediated direct reduction
• Monoamine oxidase system

Correct Answer: NADH-dependent cytochrome b5 reductase system

Q18. Which analytical technique is commonly used in forensic toxicology to detect nitrite or nitrate residues?

• Co-oximetry only
• Chromatographic and spectrometric methods (e.g., LC or GC coupled with appropriate detectors)
• Simple pH paper testing
• Direct microscopy of blood smears

Correct Answer: Chromatographic and spectrometric methods (e.g., LC or GC coupled with appropriate detectors)

Q19. Interaction caution: Methylene blue can precipitate which clinical syndrome when combined with serotonergic agents?

• Neuroleptic malignant syndrome
• Serotonin syndrome
• Acute adrenal crisis
• Anticholinergic poisoning

Correct Answer: Serotonin syndrome

Q20. Which statement about sodium nitrite chemistry is correct?

• Sodium nitrite is a strong reducing agent
• Sodium nitrite is an oxidizing agent capable of oxidizing hemoglobin
• Sodium nitrite is inert and non-reactive in biological systems
• Sodium nitrite converts to elemental nitrogen in the body

Correct Answer: Sodium nitrite is an oxidizing agent capable of oxidizing hemoglobin

Q21. Formation of carcinogenic nitrosamines from nitrites requires the presence of:

• Primary alcohols only
• Secondary amines or amides under nitrosating conditions
• High concentrations of vitamin C exclusively
• Pure oxygen atmosphere only

Correct Answer: Secondary amines or amides under nitrosating conditions

Q22. In cases where methylene blue is contraindicated or ineffective, which supportive therapy may be considered?

• Exchange transfusion or hyperbaric oxygen in severe refractory cases
• Oral iron supplementation immediately
• Intravenous insulin infusion
• Topical application of antioxidants

Correct Answer: Exchange transfusion or hyperbaric oxygen in severe refractory cases

Q23. Why are infants more at risk of nitrite-induced methemoglobinemia from contaminated water or formula?

• They have an excess of adult hemoglobin that resists oxidation
• They have lower levels of reductase enzymes and higher fetal hemoglobin susceptibility
• Their kidneys rapidly excrete nitrite preventing toxicity
• Infants have enhanced NADPH availability reducing methemoglobin faster

Correct Answer: They have lower levels of reductase enzymes and higher fetal hemoglobin susceptibility

Q24. Which one of these signs is most specifically suggestive of methemoglobinemia rather than simple hypoxemia?

• Rapid improvement with supplemental oxygen alone
• Persistent cyanosis despite high inspired oxygen concentration
• Chest pain relieved by oxygen
• Increased respiratory rate improving SpO2 readings

Correct Answer: Persistent cyanosis despite high inspired oxygen concentration

Q25. Which blood gas parameter remains relatively normal in methemoglobinemia despite clinical hypoxia?

• Arterial oxygen tension (PaO2)
• Methemoglobin percentage
• Oxygen content (CaO2)
• Hemoglobin concentration

Correct Answer: Arterial oxygen tension (PaO2)

Q26. Which preventive measure is important in reducing accidental nitrite exposure in food?

• Complete elimination of all preservatives from food
• Strict regulation of nitrite levels and good manufacturing practices
• Encouraging consumption of raw meat only
• Adding secondary amines to prevent nitrosation

Correct Answer: Strict regulation of nitrite levels and good manufacturing practices

Q27. In a laboratory context, methemoglobin causes a characteristic change in which visible property of blood?

• Blood becomes bright fluorescent under UV
• Blood turns chocolate brown and does not change color on oxygenation
• Blood becomes highly viscous
• Blood shows rapid clot formation

Correct Answer: Blood turns chocolate brown and does not change color on oxygenation

Q28. Which occupational safety measure reduces risk of nitrite exposure?

• Using local exhaust ventilation and appropriate personal protective equipment
• Relying solely on occasional handwashing
• Wearing regular street clothes in processing areas
• Eating in areas where chemicals are handled to reduce absorption

Correct Answer: Using local exhaust ventilation and appropriate personal protective equipment

Q29. Which statement about sodium nitrite as a food additive is accurate?

• It is universally banned in all countries
• It is used to inhibit Clostridium botulinum growth and impart cured color, under regulated limits
• It has no preservative effect and is purely cosmetic
• It is an essential nutrient added to infant formula

Correct Answer: It is used to inhibit Clostridium botulinum growth and impart cured color, under regulated limits

Q30. Which testing sample is often analyzed in forensic cases of suspected nitrite poisoning?

• Hair alone without other tissues
• Blood, gastric contents, and sometimes urine
• Only saliva swabs
• Nail clippings exclusively

Correct Answer: Blood, gastric contents, and sometimes urine

Q31. Which redox change describes methemoglobin formation?

• Ferric (Fe3+) to ferrous (Fe2+) conversion
• Ferrous (Fe2+) to ferric (Fe3+) conversion
• Heme nitrogen oxidation without iron change
• Loss of porphyrin ring electrons only

Correct Answer: Ferrous (Fe2+) to ferric (Fe3+) conversion

Q32. Which clinical manifestation commonly results from moderate to severe methemoglobinemia?

• Severe hyperthermia without hypoxia
• Central cyanosis and signs of tissue hypoxia such as confusion and tachycardia
• Peripheral neuropathy as the earliest sign
• Isolated jaundice only

Correct Answer: Central cyanosis and signs of tissue hypoxia such as confusion and tachycardia

Q33. Which laboratory parameter directly measures dysfunctional hemoglobin species rather than oxygen tension?

• Pulse oximetry
• Co-oximetry with fractional hemoglobin species measurement
• Serum lactate only
• Complete blood count alone

Correct Answer: Co-oximetry with fractional hemoglobin species measurement

Q34. Which of the following best describes a safe educational approach to prevent sodium nitrite misuse?

• Restricting pharmacist education about toxicology
• Clear labeling, secure storage, and public awareness about toxicity risks
• Encouraging unrestricted sale without guidance
• Promoting household use of industrial-grade nitrite

Correct Answer: Clear labeling, secure storage, and public awareness about toxicity risks

Q35. Which medication class may increase susceptibility to methemoglobinemia when combined with nitrites?

• Certain topical and local anesthetics (e.g., benzocaine) and some oxidant drugs
• All beta-blockers uniformly
• Short-acting insulin formulations
• Antacids exclusively

Correct Answer: Certain topical and local anesthetics (e.g., benzocaine) and some oxidant drugs

Q36. Which procedural monitoring is important after administering antidotal therapy for methemoglobinemia?

• Serial measurement of methemoglobin fraction and clinical status
• Measuring only blood glucose levels
• Checking urine ketones hourly
• Assessing liver enzymes only after one week

Correct Answer: Serial measurement of methemoglobin fraction and clinical status

Q37. Which factor increases the risk of nitrosamine formation in food containing nitrite?

• Presence of antioxidants such as vitamin C only
• Presence of secondary amines and high-temperature cooking
• Low temperature storage exclusively
• Absence of amines entirely

Correct Answer: Presence of secondary amines and high-temperature cooking

Q38. Which statement about sodium nitrite absorption is generally correct?

• It is not absorbed at all through the gastrointestinal tract
• It is absorbed systemically after oral ingestion and can cause rapid systemic effects
• It only affects local gut flora without systemic distribution
• It is immediately metabolized into harmless compounds in the stomach

Correct Answer: It is absorbed systemically after oral ingestion and can cause rapid systemic effects

Q39. Which is an appropriate laboratory indicator of systemic oxidative stress related to nitrite exposure?

• Elevated methemoglobin fraction and possibly elevated lactate from tissue hypoxia
• Isolated elevated serum sodium only
• Decreased creatinine clearance exclusively
• Marked increase in serum cholesterol

Correct Answer: Elevated methemoglobin fraction and possibly elevated lactate from tissue hypoxia

Q40. What is a major clinical precaution when considering methylene blue therapy?

• It is safe in all enzymatic deficiencies
• Assess for G6PD deficiency and serotonergic medications before use
• Simultaneously use with high-dose vitamin K for synergy
• Administer without monitoring as a one-time intervention

Correct Answer: Assess for G6PD deficiency and serotonergic medications before use

Q41. Which of the following best describes the difference between nitrate and nitrite in relation to methemoglobinemia?

• Nitrate is more potent at directly oxidizing hemoglobin than nitrite
• Nitrite directly oxidizes hemoglobin, while nitrate may be converted to nitrite before causing effect
• Both are inert in biological systems
• Nitrite must be converted to nitrate to be active

Correct Answer: Nitrite directly oxidizes hemoglobin, while nitrate may be converted to nitrite before causing effect

Q42. Which sign would most likely prompt urgent antidotal treatment in methemoglobinemia?

• Mild perioral dryness without cyanosis
• Marked cyanosis with altered mental status and signs of poor perfusion
• Stable vital signs with minor paleness
• Isolated mild headache that resolves spontaneously

Correct Answer: Marked cyanosis with altered mental status and signs of poor perfusion

Q43. In the context of laboratory evaluation, why is it important for B.Pharm students to differentiate pulse oximetry from co-oximetry?

• Both measure the same parameter with equal accuracy
• Pulse oximetry cannot distinguish methemoglobin from oxy- and deoxyhemoglobin, while co-oximetry can
• Co-oximetry is obsolete and rarely used
• Pulse oximetry directly measures methemoglobin fraction

Correct Answer: Pulse oximetry cannot distinguish methemoglobin from oxy- and deoxyhemoglobin, while co-oximetry can

Q44. Which regulatory consideration is relevant for pharmacists regarding sodium nitrite?

• No regulation exists for industrial-grade nitrite
• Pharmacists should be aware of its dual role as a regulated food additive and an industrial chemical with toxicity risks
• It is classified as a harmless household compound
• It is only relevant to veterinary practice and not pharmacy

Correct Answer: Pharmacists should be aware of its dual role as a regulated food additive and an industrial chemical with toxicity risks

Q45. Which clinical scenario is least consistent with methemoglobinemia?

• Patient with cyanosis unresponsive to oxygen and chocolate-brown blood
• Patient with normal PaO2 but low SpO2 readings and confusion
• Patient with high fever and purulent sputum but normal oxygenation and no cyanosis
• Infant with recent consumption of well water and rapid onset cyanosis

Correct Answer: Patient with high fever and purulent sputum but normal oxygenation and no cyanosis

Q46. Which precaution is recommended when handling sodium nitrite in laboratory or industrial settings?

• Use no protective measures to build tolerance
• Follow institutional safety protocols, use PPE, and avoid inhalation or skin contact
• Store it in open containers for ventilation
• Label containers only in code to prevent public awareness

Correct Answer: Follow institutional safety protocols, use PPE, and avoid inhalation or skin contact

Q47. Which adverse hematologic effect can occur in G6PD-deficient patients treated with methylene blue?

• Severe hemolysis
• Polycythemia vera
• Thrombocytosis only
• Leukemoid reaction exclusively

Correct Answer: Severe hemolysis

Q48. Which monitoring parameter best reflects improvement after antidotal therapy for methemoglobinemia?

• Decrease in measured methemoglobin fraction by co-oximetry and clinical improvement
• Increase in pulse rate alone
• Rise in body temperature only
• Increase in urinary protein excretion

Correct Answer: Decrease in measured methemoglobin fraction by co-oximetry and clinical improvement

Q49. Which statement about sodium nitrite labeling and public health is correct?

• Clear labeling and education help minimize accidental ingestion and misuse
• Labels are unnecessary because toxicity is negligible
• Hiding labels reduces intentional misuse
• Public access to technical manufacturing data should be unrestricted

Correct Answer: Clear labeling and education help minimize accidental ingestion and misuse

Q50. For B.Pharm students, which concise summary best captures the management priorities in sodium nitrite poisoning?

• Ignore supportive care and rely solely on antidote
• Rapid recognition of methemoglobinemia, supportive measures (oxygen, decontamination when appropriate), and timely antidotal therapy with attention to contraindications
• Immediate use of antibiotics to prevent infection
• Delay treatment until laboratory confirmation always

Correct Answer: Rapid recognition of methemoglobinemia, supportive measures (oxygen, decontamination when appropriate), and timely antidotal therapy with attention to contraindications