Poisons with methemoglobin-producing agents

Question 1

Mechanism of methemoglobin?

Answer 1

Reversible changes of the structure of hemoglobin (Fe²⁺) to methemoglobin (Fe³⁺), which can’t transport O_2.

Damage of the RBCs –> possible Heinz bodies ==> hemolysis ==> anuria

Question 2

Mechanism of verdoglobin?

Answer 2

Irreversible changes. Oxidation and splitting of the porphyrin ring.

Damage of the RBCs –> possible Heinz bodies ==> hemolysis ==> anuria

Question 3

Severity?

Answer 3

20% of Methemoglobin ==> symptoms of hypoxemia

60-80% of Methemoglobin ==> death

Question 4

NADPH-dependent enzymatic reduction of methemoglobin

Answer 4

Question 5

What is the classification of methemoglobin-producing agents?

Answer 5

Question 6

Mechanism of action of nitrites or nitrates?

Answer 6

Equimolar forming of methemoglobin

No production of verdoglobin, thus no RBC damage

Question 7

Mechanism of action of aromatic amino and nitro compounds?

Answer 7

Non-equimolar forming of methemoglobin

Question 8

Symptoms?

Answer 8

• Cyanosis
• Hypoxia
• Collapse
• In case of oxidizing agents: oliguria –> anuria –> uremia

Question 9

Therapy?

Answer 9

• 10ml 1-2% methylene blue
• 10ml 0.2% thionin
• 20ml 4% toluidine blue

Balance at 8% Hb. Fe³⁺