Is Methylene Blue SafeIn Patients With Methemoglobinemia

And Glucose 6-phosphateDehydrogenase (G6PD) Deficiency?

Bob Hoffman

New York City Poison Center, NY, USA

Overview

• 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 Reduced Oxidant

Glutathione

Sulfhydryls

Ascorbate

Catalase

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+

FeN

N

N

N

histidine O2- Oxyhemoglobin

C O COHb

OH

HMethemoglobin

Physiology

The oxidant is reduced by Hb (forming MetHb) • Then MetHb is reduced back to Hb

MetHb Reduced Hb

NADH MetHb reductase (67%)

Ascorbate (15%)

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

• 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?

• 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.

• 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 G6PD-deficient patient on experimental anticancer drug Triapine. Am J Hematol 2006;81:210-1.

• 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 life-

threatening 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