The Power Course

Methemoglobinemia which is correct


1 ) Conversion of ferous to ferric ions
2 ) Oxygen dissociation curve is shifted to the right, (decreased affinity of oxygen)
3 ) Crystalline penicillin my cause methemoglobinemia.
4 ) None of the above


Methemoglobinemia is the conversion of F2+ (ferrous)  of hemoglobin to F3+ (ferric) ion. 

Ferric ion does not bind to oxygen so there decreased oxygen-carrying capacity.

In methemoglobinemia, the oxygen dissociation curve is shifted to left, (increased affinity of oxygen) oxygen is not released at the tissue leading to tissue hypoxia.

Methemoglobinemia may be congenital ie. autosomal recessive inheritance and secondary to drugs and chemical positioning  

Acquired methemoglobinemia

This comment form. Due to Benzocaine and prilocaine, nitrates, aniline, and dapsone

Congenital methemoglobinemia

Normally some conversion of ferrous to ferric happens (1% of hemoglobin is methemoglobin) but this reversed by an enzyme system, the dihydronicotinamide adenine dinucleotide (NADH)-methemoglobin reductase system present in the RBC. congenital absence of this enzyme by inheritance can lead methemoglobinemia

Clinical features

Methemoglobin is dark-colored, and when it is present in large quantities in the circulation, it causes a dusky discoloration of the skin resembling cyanosis. 


Removal of inciting agent.

The antidote is methylene blue (tetramethylthionine chloride).


Conversion of ferous to ferric ions

Further Reading

Last Modified : 25-Dec-2019

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