Is Methylene Blue Safe
In Patients With Methemoglobinemia
And Glucose 6-phosphate
Dehydrogenase (G6PD) Deficiency?
Bob Hoffman
New York City Poison Center,
NY, USA
Overview
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Review of G6PD deficiency
Review of methemoglobinemia (very brief)
Review of methylene blue (MB) (brief)
Attempt to answer the question
– Expert opinion
– Case reports
– In Vitro data
Introduction
• G6PD deficiency – one of the most
common inherited disorders, 400 million
people affected
– Largely in tropical and subtropical countries
• Selection advantages
– Against Plasmodium falciparum infection
• Most affected individuals asymptomatic,
but the risk of acute hemolysis is well
known
Frequency of G6PD deficiency
Genetics
• > 400 variants described
• Different electrophoretic mobility, kinetic
properties.
• 5 classes according to the residual enzyme
activity based (WHO).
• Mediterranean and African (A-) variants
– The most clinically significant.
• Activity scarcely detectable in the Mediterranean
type but close to normal in the African variant.
Inheritance of G6PD Deficiency
What Do We Need G6PD For?
• Phosphogluconate pathway
• Pentose phosphate pathway
• Hexose monophosphate pathway
• Hexose monosphosphate shunt
G6PD
Catalyzes the first step in the
pentose phosphate pathway
Regulatory enzyme
The enzyme is highly specific for NADP+; the
Km for NAD+ is 1000 greater than for NADP+.
Pentose Phosphate Yields
• Ribulose (ribose) 5-phosphate
– Essential nucleotide in biosynthesis
leading to:
• DNA
• RNA
• Various cofactors
–CoA, FAD, SAM, NAD+/NADP+
Glutathione
reductase uses
NADPH as a
cofactor to
reduce GSSG
back to two
moles of GSH.
G6PD Deficiency
• G6PD deficiency is not the absence of
G6PD, it is a decreased activity
– Many cells express G6PD
– Red cells are the only important cell line
because they lack a nucleus
– Activity of G6PD highest (normal) in young
erythrocytes and decreases with aging
– Oxidants preferentially destroy senescent red
blood cells
Response to Oxidants
Oxidant Response
• If not reduced:
– Some produce hemolysis
• Oxidation of the hemoglobin chain
– Some produce MetHb
• Oxidation of iron
– Some produce both?
Physiology
• Direct reduction of the oxidant
Oxidant
Glutathione
Sulfhydryls
Ascorbate
Catalase
Reduced Oxidant
RBCs with Heinz Bodies
• Precipitation of
hemoglobin due to
disulfide bond formation
between Hb molecues
• Upper photo shows
distorted RBCs with
large Heinz bodies
• Bottom photo shows
RBC stained with
methylene blue
Methemoglobin Definition
• Oxidation of the iron molecule in
hemoglobin from its normal Fe2+ to Fe3+
N
N
Fe
histidine
N
N
O
H
Methemoglobin
H
O2- Oxyhemoglobin
C O
COHb
Physiology
The oxidant is reduced by Hb (forming MetHb)
• Then MetHb is reduced back to Hb
MetHb
NADH MetHb reductase (67%)
Ascorbate (15%)
Reduced Hb
Glutathione (12%)
NADPH Met Hb reductase (5%)
Can You Use Methylene Blue In
Patients with G6PD Deficiency?
Famous Textbook Quotes
• Methylene blue remains the first line therapy
even in patients with known G6PD deficiency
– Brent
• Should never be administered to someone with
known G6PD deficiency
– Shannon
• Should be used cautiously in patients with G6PD
deficiency
– Dart
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28 year old man
Ingested 60-120mL of 18% aniline
MetHb 11 gm/dL (70-80%)
75 mg methylene blue given
Didn’t get better
G6PD screening showed deficiency (A-)
Given ascorbate
Hemolyzed, Hb fell, recovered
– Rosen PJ: Failure of methylene blue treatment in toxic
methemoglobinemia. Association with glucose-6-phosphate
dehydrogenase deficiency. Ann Intern Med 1971;75:83-6
What
happened
between the
0 and 4 hour
levels?
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26 month, 9.8-kg boy with G6PD deficiency
Ingested 90 mL of nitroethane – MetHb 23.3%
MetHb rises to 37%, then over 40%
Cyanotic, in respiratory failure, intubated
Two doses of methylene blue (2mg/kg) given
“without response”
• No hemolysis
• Finally treated with exchange transfusion
– Golden PJ: Treatment of high-risk, refractory acquired
methemoglobinemia with automated red blood cell exchange. J
Clin Apher 1998;13:28-31.
• 74 G6PD deficient men
• 3 day regimen
– Chloroquine 1500 mg
– Methylene blue 780 mg (mg/kg PO BID)
• No hemolysis occurred
– Mandi G: Safety of the combination of chloroquine and
methylene blue in healthy adult men with G6PD deficiency from
rural Burkina Faso. Trop Med Int Health. 2005;10:32-8.
• 3 case reports
• Intraamniotic methylene blue given for
PROM (2); IV for maternal MetHb (1)
– Dose varied
• All developed elevated bilirubin
• Only 2 G6PD deficient
– Gauthier TW: Methylene blue-induced hyperbilirubinemia in
neonatal glucose-6-phosphate dehydrogenase (G6PD)
deficiency. J Matern Fetal Med. 2000;9:252-4.
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Neonate, known G6PD deficiency
Multiple cardiac abnormalities
Undergoes surgical repair on day 28 of life
Requires nitroglycerin IV
Develops MetHb: 75%
Given low dose (0.1 mg/kg) methylene blue
Has mild hemolysis requiring no therapy
– Middali MM: Postoperative methemoglobinemia with
associated G-6-P-D deficiency in infant cardiac
surgery--enigmas in diagnosis and management.
Paediatr Anaesth 2005;15:334-7.
• 59-year-old man with metastatic renal cell CA
• Trial of 3-aminopyridine-2-carboxaldehyde
thiosemicarbazone (3-AP; Triapine)
• Developed MetHb 35%
• Given 3 doses (1 mg/kg) methylene blue
• MetHb fell to 10%, then 6.5 %
• Masive hemolysis
• Severe G6PD deficiency confirmed later
– Foltz LM: Recognition and management of
methemoglobinemia and hemolysis in a G6PDdeficient patient on experimental anticancer drug
Triapine. Am J Hematol 2006;81:210-1.
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Metoclopramide 10 mg administered twice
Cyanosis and dyspnea; 28 hours later
MetHb was 43%
Ascorbic acid 150 mg and methylene blue 60
mg given
Consciousness deteriorated
Methylene blue 40 mg was repeated at 2 hours
Deteriorated rapidly and he died 12 hours
Blood taken a before death was hemolysed
Postmortem: b5R and severely G6PD deficient
– Karadsheh NS: Metoclopramide-induced methemoglobinemia in a
patient with co-existing deficiency of glucose-6-phosphate
dehydrogenase and NADH-cytochrome b5 reductase: failure of
methylene blue treatment Haematologica 2001;86:659
• 25 year old man; large dermal exposure to
aniline
• 5 hours later – MetHb 51%
• Methylene blue 40mg IV improved symptoms
• MetHb fell to 2.1%
• Developed significant hemolysis
• G6PD deficient
• Recovered (transfused)
– Liao YP: Hemolytic anemia after methylene blue therapy for
aniline-induced methemoglobinemia. Vet Hum Toxicol.
2002;44:19-21.
In Vivo Summary
• Does Methylene blue fail?
– Often works
– Usually slowly
• Does methylene blue cause hemolysis
– It can, and it can be severe
– Especially when hemolysis is present prior to
therapy
Beutler E: Methemoglobin Reduction: Studies of
the interaction between cell popluations and of the
role of methylene blue. Blood 1963;22:323-333
• Incubated human RBCs with nitrite to
induce MetHb
• Treated with methylene blue and glucose
• Observed rates of fall
– Normal cells
– G6PD cells (A-)
– Mixture of cells
Implications
• G6PD deficient cells clear MetHb slowly in
response to methylene blue
• Either NADPH or leukomethylene blue can
move from healthy cells to deficient cells
• This effect is more pronounced at lower
levels of MetHb
– Young cells and reticulocytes are G6PD
present
– Role of transfusion (fresh blood)?
Summary (1)
• Data on the use of methylene blue in
patients with G6PD deficiency are limited
– Most support some degree of efficacy
– Significant risk of hemolysis
• Would administer methylene blue in:
– Patients with no history of G6PD deficiency
– Patients with known G6PD deficiency and lifethreatening MetHb
• Ascorbate, Exchange transfusion, HBO, NAC
Summary (2)
• Withhold methylene blue in:
– Patients with known severe variant G6PD
deficiency (Mediterranean) not significantly ill
– Patients with known or suspected G6PD
deficiency and marginal indications for
treatment
– Patients with significant active hemolysis in
addition to MetHb
Summary (3)
• If giving methylene blue to patients with a
known or suspected history of G6PD
deficiency
– Keep the first dose small (1 mg/kg)
– Recheck the MetHb often
– Do not repeat if unsuccessful
– Observe closely for hemoylsis