Failure of methylene blue treatment in toxic methemoglobinemia. Association with glucose-6-phosphate dehydrogenase deficiency

Exploring the Possible Link Between Diabetic Ketoacidosis, Glucose-6-Phosphate Dehydrogenase Deficiency, and Methemoglobinemia

One of the most widespread enzymopathies affecting human beings is glucose-6-phosphate dehydrogenase (G6PD) deficiency, which is brought on by inherited mutations in the X-linked gene. Red blood cells (RBCs) with a G6PD deficiency are more sensitive to oxidative assault and consequently to hemolysis. There are more than 200 known G6PD mutations, of which around half are polymorphic and thus prevalent in a variety of populations. We present a case of diabetic ketoacidosis (DKA), with severe hemolytic anemia and methemoglobinemia. The patient was admitted to the intensive care unit, treated for DKA, and received a blood transfusion. In addition, the patient presented with high methemoglobin levels and features of severe hemolytic anemia from the onset, which made the diagnostic consideration of G6PD highly likely. Accordingly, the patient was treated with several doses of ascorbic acid instead of methylene blue. In a nutshell, a patient with DKA who has hemolytic anemia has to have it properly evaluated and controlled. The link between methemoglobinemia, G6PD deficiency, and DKA should be recognized by medical professionals, particularly when oxygen saturation gaps are found.

A Case Report of Primaquine Associated Methemoglobinemia in a Man With Pneumocystis Jirovecii Pneumonia Following Cardiac and Renal Transplantation

We describe the case of a 51-year-old Caucasian man with a background of a cardiac and renal transplant who developed Enterocytozoon bieneusi colitis and pneumocystis jirovecii (PJP) pneumonia following treatment for suspected rejection. The patient developed methemoglobinemia which was attributed to primaquine. He was treated with intravenous methylene blue leading to clinical and biochemical resolution. We describe in detail the pathophysiological mechanism for methemoglobinemia and its treatment, in particular with methylene blue.

Phenazopyridine-Induced Methemoglobinemia in a Jehovah's Witness Treated with High-Dose Ascorbic Acid Due to Methylene Blue Contradictions: A Case Report and Review of the Literature

Methemoglobinemia is an acute medical emergency that requires prompt correction. Physicians should have a high degree of suspicion of methemoglobinemia in cases that present with hypoxemia that does not resolve with supplemental oxygenation, and they should confirm this suspicion with a positive methemoglobin concentration on arterial blood gas. There are multiple medications that can induce methemoglobinemia, such as local anesthetics, antimalarials, and dapsone. Phenazopyridine is an azo dye used over-the-counter as a urinary analgesic for women with urinary tract infections, and it has also been implicated in causing methemoglobinemia. The preferred treatment of methemoglobinemia is methylene blue, but its use is contraindicated for patients with glucose-6-phosphatase deficiency or those who take serotonergic drugs. Alternative treatments include high-dose ascorbic acid, exchange transfusion therapy, and hyperbaric oxygenation. The authors report a case of a 39-year-old female who took phenazopyridine for 2 weeks to treat dysuria from a urinary tract infection and subsequently developed methemoglobinemia. The patient had contraindications for the use of methylene blue and was therefore treated with high-dose ascorbic acid. The authors hope that this interesting case promotes further research into the utilization of high-dose ascorbic acid for managing methemoglobinemia in patients who are unable to receive methylene blue.

A Case of Cyanosis With Saturation Gap: Dapsone-Induced Methemoglobinemia

Dapsone is an antibiotic used in the management of dermatologic infections and opportunistic infection prophylaxis in developed countries. Methemoglobinemia (MetHb) is a known complication of dapsone use that can result in cyanosis. MetHb is an aberrant form of hemoglobin produced physiologically by auto-oxidation. An impairment in the process of auto-oxidation due to genetic defects or the use of drugs/toxins causes its levels to rise. Management involves timely recognition and the use of methylene blue (MB) or ascorbic acid. We describe the diagnosis and management of a patient with acquired MetHb as a result of dapsone use.

Elevated methemoglobin levels in patients treated with hydroxocobalamin: a case series and in-vitro analysis

BACKGROUND

Historically, the first step in treating cyanide (CN^-) toxicity utilized antidotes to induce methemoglobinemia. This is concerning in patients who are already hypoxemic or have elevated carboxyhemoglobin. Hydroxocobalamin (OHCbl) is now the first-line antidote for CN^- toxicity and is not known to induce methemoglobinemia. We observed elevated methemoglobin (MetHb) levels in several patients treated with OHCbl and sought to investigate the incidence of MetHb formation following administration of OHCbl.

METHODS

Chart review: A single-center, retrospective case series of patients who received 5 or 10 g of hydroxocobalamin from 01/01/2011 through 04/30/2019. Data was analyzed using descriptive statistics. In-vitro study: Discarded blood was separated into whole blood and plasma samples. OHCbl and normal saline was added to reach 0×, 1×, 2×, and 4× peak therapeutic concentrations and analyzed at times 0, 2, and 4 h after administration.

RESULTS

Chart review: Twenty-seven cases of OHCbl administration were identified. The median age was 53 years (IQR 38 - 64) and 20 (74.1%) were male. Exposure to a house fire or smoke inhalation was the reason for OHCbl administration in 21 (77.8%) patients. Five (18.5%) patients received 10 g of OHCbl while the rest received 5 g. Six (22.2%) patients developed methemoglobinemia, all after 5 g OHCbl administration; four had been exposed to fire and smoke, two received the medication for severe acidosis of unknown etiology not related to fire or smoke. The median peak level was 7.1% (IQR 2.2 - 16.4%) at a median time of 11.4 h post-administration. Two patients received methylene blue (MB), neither responded. Death occurred in 17 (63%) cases. In-vitro study: We observed a dose dependent elevation in total hemoglobin but did not detect any increase in MetHb.

CONCLUSION

We observed a noteworthy temporal association between the formation of methemoglobinemia and the administration of hydroxocobalamin. This does not appear to be an artifact of the CO-oximeters. This could have profound implications for patients who are already hypoxemic or have impaired oxygen carrying capacity from carboxyhemoglobin.

Two cases of methaemoglobinaemia and haemolysis due to poisoning after skin absorption of 4-chloro-1-nitrobenzene

INTRODUCTION

While 4-chloro-1-nitrobenzene has oxidising properties and can lead to methaemoglobinaemia and haemolysis, such reports are rare. We herein describe two cases of 4-chloro-1-nitrobenzene poisoning after skin exposure and detail relevant clinical characteristics and treatment outcomes.

CASE PRESENTATION

A 45-year-old man and his 32-year-old male co-worker presented at our department shortly after skin exposure to 4-chloro-1-nitrobenzene. They developed similar symptoms, including dizziness, dyspnoea, excessive fatigue, and coma. Patients' chest inspection yielded normal findings. Despite maximal oxygen supplementation, neither patient exhibited improvements in the following clinical parameters: diffuse cyanosis, chocolate-coloured blood, and decreased pulse oximetry. For patients 1 and 2, methaemoglobin levels at admission were 78.6% and 63.6%, and 4-chloro-1-nitrobenzene concentrations were 4.12 μg/mL and 2.89 μg/mL, respectively. Their symptoms and methaemoglobin levels improved after we cautiously administered methylene blue; we subsequently detected oxidative haemolysis (confirmed by peripheral blood smears) that later resolved without further aggravation. No further episodes of anaemia were documented via telephone follow-up for eight months after hospital discharge for either patient.

DISCUSSION

Typical features of methaemoglobinaemia included diffuse cyanosis, dark chocolate-coloured blood, elevated partial pressure of oxygen, and decreased pulse oximetry saturation. Haemolysis likely occurred secondary to the toxic effects of 4-chloro-1-nitrobenzene.

Acquired methemoglobinemia in children presenting to Italian pediatric emergency departments: a multicenter report

INTRODUCTION

Methemoglobinemia (MetHb) is a rare inherited or acquired cause of cyanosis in children. Owing to its rarity, case reports and case series are mostly available in the current literature. This study reports data on a large sample of children with acquired MetHb.

METHODS

Data on patients admitted for acquired MetHb between January 2007 to December 2020 was extracted from the databases of five Italian pediatric emergency departments (EDs). Demographical and clinical characteristics was reported and discussed.

RESULTS

Nineteen cases of acquired MetHb were evaluated. Ten patients (52.6%) were male and 9 (47.4%) were female. The median age was 8.23 months. The median time from trigger to symptom onset was 6 hours. Mostly, the intoxication presumptively occurred by home ingestion of contaminated food, mainly badly preserved vegetable broth. All patients were cyanotic at admission, most patients also presented tachycardia and/or tachypnea, and two patients were comatose. Antidotal therapy with methylene blue was given in 14 patients (73.7%). The median hospital stay was 2 days. All patients survived.

DISCUSSION

As MetHb leads to the pathognomonic brown blood discoloration, blood gas analysis is mandatory immediately upon hospital arrival of a cyanotic patient. A correct medical history is crucial to identify the trigger and remove it. In our sample, the age onset was much lower than in the previous literature, and MetHb mainly due to ingestion of contaminated vegetable broth. Methylene blue led to a rapid recovery in all patients. Oxygen therapy may well lead to complete recovery when methemoglobin levels do not exceed 30% in asymptomatic and 20% in mildly symptomatic patients.

CONCLUSIONS

The diagnosis and management of acquired MetHb in the emergency setting requires acknowledgment of this condition as a cause of cyanosis in the weaning child. Indeed, when promptly recognized and treated, this severe condition rapidly resolves with no significant acute sequelae.

Recommendations for diagnosis and treatment of methemoglobinemia

Methemoglobinemia is a rare disorder associated with oxidization of divalent ferro‐iron of hemoglobin (Hb) to ferri‐iron of methemoglobin (MetHb). Methemoglobinemia can result from either inherited or acquired processes. Acquired forms are the most common, mainly due to the exposure to substances that cause oxidation of the Hb both directly or indirectly. Inherited forms are due either to autosomal recessive variants in the CYB5R3 gene or to autosomal dominant variants in the globin genes, collectively known as HbM disease. Our recommendations are based on a systematic literature search. A series of questions regarding the key signs and symptoms, the methods for diagnosis, the clinical management in neonatal/childhood/adulthood period, and the therapeutic approach of methemoglobinemia were formulated and the relative recommendations were produced. An agreement was obtained using a Delphi‐like approach and the experts panel reached a final consensus >75% of agreement for all the questions.

A Case Report of Acute Transient Encephalopathy Following a Trans-esophageal Echocardiography

Methemoglobinemia is caused due to an increase in methemoglobin in the blood, impairing oxygen transfer to tissues. Acquired methemoglobinemia is caused by various drugs like local anesthetics, antibiotics, nitrates, nitrites, and food additives. We present a case of a 73-year-old male who presented with cyanosis, altered mental status, and hypoxia following transesophageal echocardiography. Arterial blood gas analysis revealed methemoglobinemia. He had been given topical lidocaine and benzocaine spray before the procedure. He improved after the administration of methylene blue. The case highlights the importance of considering methemoglobinemia in patients presenting with cyanosis, altered mental status, and hypoxia after endoscopic procedures.

Methemoglobin formation in mutant hemoglobin α chains: electron transfer parameters and rates

Hemoglobin-mediated transport of dioxygen (O₂) critically depends on the stability of the reduced (Fe²⁺) form of the heme cofactors. Some protein mutations stabilize the oxidized (Fe³⁺) state (methemoglobin, Hb M), causing methemoglobinemia, and can be lethal above 30%. The majority of the analyses of factors influencing Hb oxidation are retrospective and give insights only for inner-sphere mutations of heme (His58, His87). Herein, we report the first all-atom molecular dynamics simulations on both redox states and calculations of the Marcus electron transfer (ET) parameters for the α chain Hb oxidation and reduction rates for Hb M. The Hb wild-type (WT) and most of the studied α chain variants maintain globin structure except the Hb M Iwate (H87Y). The mutants forming Hb M tend to have lower redox potentials and thus stabilize the oxidized (Fe³⁺) state (in particular, the Hb Miyagi variant with K61E mutation). Solvent reorganization (λ_solv 73-96%) makes major contributions to reorganization free energy, whereas protein reorganization (λ_prot) accounts for 27-30% except for the Miyagi and J-Buda variants (λ_prot ∼4%). Analysis of heme-solvent H-bonding interactions among variants provide insights into the role of Lys61 residue in stabilizing the Fe²⁺ state. Semiclassical Marcus ET theory-based calculations predict experimental k_ET for the Cyt b5-Hb complex and provide insights into relative reduction rates for Hb M in Hb variants. Thus, our methodology provides a rationale for the effect of mutations on the structure, stability, and Hb oxidation reduction rates and has potential for identification of mutations that result in methemoglobinemia.

Glucose-6-Phosphate Dehydrogenase Deficiency-Associated Hemolytic Anemia and Methemoglobinemia in a Patient Treated With Hydroxychloroquine in the Era of COVID-19

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common enzymatic disorder of red blood cells worldwide. The severity of hemolytic anemia varies among individuals with G6PD deficiency, depending on the genetic variant in the G6PD gene; this makes the diagnosis of the condition more challenging in some cases. In this report, we present a case of severe hemolytic anemia and methemoglobinemia in a patient with G6PD deficiency who had been exposed to hydroxychloroquine prescribed for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. To the best of our knowledge and based on a literature search, this is one of the first case reports in the literature about hemolytic crisis and methemoglobinemia in a patient with critical illness due to severe coronavirus disease 2019 (COVID-19) who was exposed to hydroxychloroquine. It is critical for physicians and caregivers to recognize the effects of oxidative stressors such as hydroxychloroquine, particularly in this era of the COVID-19 pandemic and in regions with a high prevalence of G6PD deficiency, for the appropriate management of this unique subset of patients.

The Role of Methemoglobin and Carboxyhemoglobin in COVID-19: A Review

Following the outbreak of a novel coronavirus (SARS-CoV-2) associated with pneumonia in China (Corona Virus Disease 2019, COVID-19) at the end of 2019, the world is currently facing a global pandemic of infections with SARS-CoV-2 and cases of COVID-19. Since severely ill patients often show elevated methemoglobin (MetHb) and carboxyhemoglobin (COHb) concentrations in their blood as a marker of disease severity, we aimed to summarize the currently available published study results (case reports and cross-sectional studies) on MetHb and COHb concentrations in the blood of COVID-19 patients. To this end, a systematic literature research was performed. For the case of MetHb, seven publications were identified (five case reports and two cross-sectional studies), and for the case of COHb, three studies were found (two cross-sectional studies and one case report). The findings reported in the publications show that an increase in MetHb and COHb can happen in COVID-19 patients, especially in critically ill ones, and that MetHb and COHb can increase to dangerously high levels during the course of the disease in some patients. The medications given to the patient and the patient’s glucose-6-phospate dehydrogenase (G6PD) status seem to be important factors determining the severity of the methemoglobinemia and carboxyhemoglobinemia. Therefore, G6PD status should be determined before medications such as hydroxychloroquine are administered. In conclusion, MetHb and COHb can be elevated in COVID-19 patients and should be checked routinely in order to provide adequate medical treatment as well as to avoid misinterpretation of fingertip pulse oximetry readings, which can be inaccurate and unreliable in case of elevated MetHb and COHb levels in the blood.

Elevated Methemoglobin Levels in a Patient Treated with Hydroxocobalamin After Suspected Cyanide Exposure

BACKGROUND

Cyanide (CN) toxicity commonly occurs during enclosed-space fires. Historically, the first step in treating CN toxicity utilized amyl nitrite and sodium nitrite to induce methemoglobinemia, which can be dangerous in this population. Hydroxocobalamin (OHCob), which binds to CN to form the nontoxic metabolite cyanocobalamin, is now the first-line antidote for CN toxicity, and has the advantage of not inducing methemoglobinemia.

CASE REPORT

A 62-year-old man presented to the Emergency Department (ED) after a house fire. He was intubated for respiratory distress and hypoxia with an initial carboxyhemoglobin of 1.3%, methemoglobin 0.3%, and anion gap 19. Eleven hours after presentation, his serum lactic acid was 9 mmol/L. Given his continued deterioration, 14 h after arrival he received OHCob 5 g i.v. for presumed CN toxicity. Methemoglobin concentration 4 min prior to OHCob administration was 0.7%, and 2 h after administration was 4.2%. This subsequently increased to 14.3% (16 h after OHCob administration) and peaked at 16.3% (47 h after OHCob administration), at which time he was administered a dose of methylene blue 50 mg i.v., 60 h after ED arrival. His methemoglobin concentrations fluctuated until a consistent downward trend starting at 92 h from ED arrival. He continued to deteriorate and expired on hospital day 5 with a methemoglobin concentration of approximately 6.0%. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: CN toxicity requires immediate recognition and treatment. The antidote, OHCob, is believed to not induce methemoglobinemia. However, this potential side effect must be considered by emergency physicians when treating suspected CN toxicity, especially if the patient does not improve after antidotal therapy.

Naphthalene Toxicity in a Three-Year-Old Child Complicated by Severe Hemolytic Anemia and Mild Methemoglobinemia: A Case Report

BACKGROUND

Exposure to naphthalene, which is widely used in mothballs, does not usually produce adverse effects. However, naphthalene can be toxic, especially in individuals with underlying conditions such as glucose-6-phosphate-dehydrogenase (G6PD) deficiency.

CASE REPORT

A 3-year-old boy was brought to our Emergency Department after accidentally ingesting naphthalene mothballs 3 days prior to presentation. Laboratory investigations revealed that he had severe hemolytic anemia and mild methemoglobinemia (6%), which were treated with ascorbic acid and N-acetylcysteine. The patient tested positive for G6PD deficiency after stabilization and completion of his treatment. All provided treatments were administered empirically; test results were available only after the patient was discharged. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Naphthalene exposure is a common pediatric presentation with various complications that can occur in certain high-risk individuals, such as those with G6PD deficiency. Emergency physicians should be aware of this to anticipate and be able to treat worsening toxicity.

Acquired methemoglobinemia presenting to the pediatric emergency department: a clinical challenge

OBJECTIVES

Acquired methemoglobinemia (MetHb) is an uncommon presentation of cyanosis in the pediatric emergency department (ED), making its diagnosis and management a clinical challenge. Through this case series we hope to improve clinician ability to recognize the potential for MetHb in pediatric ED patients and to avoid overlooking this important cause of cyanosis.

METHODS

This was a case series using a health records review, investigating patients diagnosed with MetHb at our pediatric ED during 2007-2018. We included only cases with methemoglobin saturation ≥5%.

RESULTS

Ten patients were diagnosed with MetHb in our pediatric ED during the study period. Five had an underlying hematologic disease who received a pharmacologic trigger known to induce MetHb as well (four dapsone, one rasburicase). The other five patients were previously healthy, who presented with a clinical picture of hemolytic anemia, all of whom were diagnosed with previously unknown glucose-6-phosphate dehydrogenase (G6PD) deficiency. Two of the patients received methylene blue, and five patients needed packed red blood cells. All of the patients survived the acute MetHb episode.

CONCLUSION

Acquired MetHb in the pediatric ED is a rare but important cause of cyanosis. Diagnosis and management of acute, acquired MetHb in the ED requires a high level of suspicion, and a background knowledge of the common precipitants and underlying conditions associated with this condition. We hope this case series will help ED physicians to consider MetHb in pediatric patients presenting with cyanosis and persistent hypoxia. Exposure to known precipitants (e.g., medications and foods), particularly in the setting of active treatment for malignancy or with symptoms of hemolytic anemia should further increase suspicion.

Recent advances in transmission-blocking drugs for malaria elimination

The scientific community worldwide has realized that malaria elimination will not be possible without development of safe and effective transmission-blocking interventions. Primaquine, the only WHO recommended transmission-blocking drug, is not extensively utilized because of the toxicity issues in G6PD deficient individuals. Therefore, there is an urgent need to develop novel therapeutic interventions that can target malaria parasites and effectively block transmission. But at first, it is imperative to unravel the existing portfolio of transmission-blocking drugs. This review highlights transmission-blocking potential of current antimalarial drugs and drugs that are in various stages of clinical development. The collective analysis of the relationships between the structure and the activity of transmission-blocking drugs is expected to help in the design of new transmission-blocking antimalarials.

Diabetic Ketoacidosis Revealing Severe Glucose-6-Phosphate Dehydrogenase Deficiency (G6PD-D) Deficiency with Methemoglobinemia: A Case Report

Patient: Male, 17

Final Diagnosis: Diabetic ketoacidosis revealing severe G6PD deficiency with methemoglobinemia

Symptoms: Jaundice

Medication: —

Clinical Procedure: None

Specialty: Hematology

Acute intravascular hemolysis due to naphthalene toxicity: a case report

BACKGROUND

Naphthalene (mothball) is a commonly used deodorizer in the Indian subcontinent, including Sri Lanka. Though it is freely available around this country, poisoning has never been reported in the literature. Ingestion, either accidental or by deliberate self-harm, can occur due to its abundance as well as its candy-resembling appearance.

CASE PRESENTATION

A 33-year-old Sri Lankan woman presented to us 2 days after the self-ingestion of 15 naphthalene balls. She had features of intravascular hemolysis without features of pigment nephropathy or methemoglobinemia. She was symptomatically managed with blood transfusion and adequate hydration.

CONCLUSION

Naphthalene ingestion can lead to severe intravascular hemolysis as well as methemoglobinemia. The resultant pigment nephropathy may also lead to acute kidney injury.

Rasburicase-induced Hemolytic Anemia in an Adolescent With Unknown Glucose-6-Phosphate Dehydrogenase Deficiency

Rasburicase, used in the prevention and treatment of tumor lysis syndrome (TLS), may cause hemolytic anemia and methemoglobinemia in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency. Although routine screening for G6PD deficiency has been recommended, given the turnaround time for test results and the urgency to treat TLS, such screening may not be feasible. We report a case of rasburicase-induced hemolytic anemia without methemoglobinemia in an adolescent with T-cell lymphoblastic lymphoma, TLS, and previously unrecognized G6PD deficiency. Previous reports of hemolytic anemia with rasburicase are reviewed, mechanisms discussed, and preventative strategies presented.

Rasburicase-induced methemoglobinemia: The eyes do not see what the mind does not know

Rasburicase is indicated for the prevention and treatment of tumor lysis syndrome which can be a potentially life-threatening emergency. The drug has oxidizing potential and as an adverse effect, it can convert the ferrous form of iron in erythrocytes to its ferric form resulting in the formation of methemoglobin which makes the heme component incapable of carrying oxygen. Patients with glucose-6-phosphate dehydrogenase enzyme deficiency are at high risk of methemoglobinemia from oxidizing agents. Symptoms of methemoglobinemia range from none to life-threatening hypoxemia, cyanosis and respiratory compromise. Treatment is indicated at levels above 20% and at lower levels if the patient is significantly anemic. We present a case of a 60-year-old male with diffuse large B cell lymphoma at high risk of tumor lysis syndrome. Rasburicase was administered to prevent renal failure and further rise in uric acid. Twenty-four hours later, a bedside pulse oximetry showed an oxygen saturation ranging from 60 to 65% with minimal cyanosis. Co-oximetry revealed a methemoglobin level of 9.8%. Methylene blue was administered and the methemoglobin level decreased to 2.6%. However, the patient developed hemolysis several hours later, likely secondary to rasburicase and methylene blue, requiring transfusion support. We discuss this potentially fatal and initially asymptomatic adverse effect of rasburicase along with diagnostic and treatment considerations, and review the cases described in the current literature.

Central Nervous System Symptoms Due to Transient Methemoglobinemia in a Child With G6PD Deficiency

The authors herein report a 5-year-old child who presented with massive hemolysis, irritability, and cyanosis. The final diagnosis was glucose-6-phosphate dehydrogenase deficiency with associated central nervous system symptoms probably because of concomitantly acquired methemoglobinemia following oxidant drug exposure. The associated acute-onset anemia would have contributed to the development of cerebral anoxia-related seizures and encephalopathy.

A Case of Topical Benzocaine-Induced Methemoglobinemia

The author reports a case of topical benzocaine-induced methemoglobinemia. Benzocaine is a topical anesthetic commonly used during minor surgical and cannulation procedures. Although not widely reported, benzocaine has the potential to induce severe or life-threatening methemoglobinemia. Clinical practitioners should be cognizant of this complication associated with benzocaine use and its appropriate management. The following report describes a case of topical benzocaine-induced methemoglobinemia in a 74-year-old, Caucasian woman who had undergone transesophageal echocardiography and who received topical benzocaine for local anesthesia. Ten minutes after the administration of benzocaine, her oxygen saturation levels decreased to 71%, requiring immediate attention. Co-oximetry (multiple wavelength spectrophotometry) measured methemoglobin levels indicated the presence of methemoglobinemia. The patient was subsequently treated with 60 mg of intravenous methylene blue. Within 10 minutes, the patient’s condition had improved. The primary etiology of methemoglobinemia is from exposure to oxidizing agents. Benzocaine is an oxidizing agent commonly used as a topical anesthetic. Topically applied benzocaine, in the patient described here and in other reported cases, produced elevated methemoglobin levels requiring treatment with a reducing agent. Methylene blue, within a specified dosage range, can serve as a reducing agent to reverse the effects of topically applied benzocaine-induced methemoglobinemia.

Antidote Use in the Critically Ill Poisoned Patient

The proper use of antidotes in the intensive care setting when combined with appropriate general supportive care may reduce the morbidity and mortality associated with severe poisonings. The more commonly used antidotes that may be encountered in the intensive care unit ( N-acetylcysteine, ethanol, fomepizole, physostigmine, naloxone, flumazenil, sodium bicarbonate, octreotide, pyridoxine, cyanide antidote kit, pralidoxime, atropine, digoxin immune Fab, glucagon, calcium gluconate and chloride, deferoxamine, phytonadione, botulism antitoxin, methylene blue, and Crotaline snake antivenom) are reviewed. Proper indications for their use and knowledge of the possible adverse effects accompanying antidotal therapy will allow the physician to appropriately manage the severely poisoned patient.

A Pale Baby With Blue Blood

A previously healthy 9-month-old boy presented to the emergency department with sudden onset of pallor and reduced activity. A detailed history and initial blood tests revealed the diagnosis of oxidant stress-induced hemolysis caused by glucose-6-phosphate dehydrogenase deficiency. However, the child also had a second diagnosis that was revealed with additional testing. This case is described to illustrate the dual diagnosis and management guidelines for both potentially serious conditions.

Rasburicase-Induced Methemoglobinemia in a Patient with Aggressive Non-Hodgkin's Lymphoma

Patient: Male, 74

Final Diagnosis: Rasburicase-induced methemoglobinemia

Symptoms: Acute shortness of breath

Medication: Rasburicase

Clinical Procedure: Attempted percutaneous coronary intervention (PCI)

Specialty: Oncology

Methaemoglobinaemia in a G6PD-deficient child treated with rasburicase

A 5-year-old boy from the Congo, was admitted for hyperleucocytic acute lymphoblastic leukaemia, with a high risk of tumour lysis syndrome (TLS). He had splenomegaly and mediastinal lymphadenopathy on chest X-ray. We started steroids and hyperhydration with rasburicase to prevent TLS. Respiratory failure with mediastinal enlargement developed rapidly. A few hours after intensive care unit (ICU) admission, he was started on mechanical ventilation. Chemotherapy was started immediately given the strong suspicion of mediastinal compression. Low oxygen saturation with high partial arterial oxygen pressure persisted. Blood tests confirmed 20% methaemoglobinaemia and glucose-6-phosphate dehydrogenase (G6PD) deficiency. Allopurinol was substituted for rasburicase. The methaemoglobinaemia disappeared rapidly and he was discharged from the ICU after 72 h. In case of rasburicase use, a close clinical monitoring is mandatory, especially in populations where G6PD deficiency is highly prevalent. Methaemoglobinaemia must be suspected in case of low oxygen saturation when all other potential causes have been ruled out.

Acute intravascular hemolysis and methemoglobinemia following naphthalene ball poisoning

Naphthalene (C10H8) is a natural component of fossil fuels such as petroleum, diesel and coal. The common consumer products made from naphthalene are moth repellents, in the form of mothballs or crystals, and toilet deodorant blocks. Major toxic effects of naphthalene are due to precipitation of acute intravascular hemolysis. Very few cases of naphthalene poisoning and its effects have been reported from India. We report a case of accidental naphthalene poisoning, who presented with intravascular hemolysis and methemoglobinemia.

Methemoglobinemia in an elderly patient with glucose-6-phosphate dehydrogenase deficiency: a case report

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an X-linked genetic disorder characterized by low levels of the G6PD enzyme. It is present worldwide but with more prevalence in the Middle East and the Mediterranean areas. We report a case of severe hemolysis due to G6PD deficiency manifesting as methemoglobinemia in a 70 year old Omani male never known to have any previous hemolytic episodes or previously diagnosed of G6PD deficiency.

Acute methemoglobinemia with hemolytic anemia following bio-organic plant nutrient compound exposure: Two case reports

Two young women, were reffered to our hospital on two different occasions with history of breathlessness and mental confusion, following consumption of two different bio-organic plant nutrient compounds with a suicidal intent. On examination, they had cyanotic mucous membranes, and their blood samples showed the classic 'dark chocolate brown' appearance. Work up revealed cyanosis unresponsive to oxygen supplementation and absence of cardiopulmonary abnormality. Pulse oximetry revealed saturation of 75% in case 1 and 80% in case 2, on 8 liters oxygen supplementation via face masks, although their arterial blood gas analysis was normal, suggestive of "saturation gap". Methemoglobinemia was suspected based on these findings and was confirmed by Carbon monoxide-oximetry (CO-oximetry). Methylene blue was administered and the patients showed dramatic improvement. Both the patients developed evidence of hemolysis approximately 72 hours following admission which improved with blood transfusion and supportive treatment. The patients were eventually discharged without any neurological sequalae.

Plasmodium falciparum gametocytes: with a view to a kill

Drugs that kill or inhibit the sexual stages of Plasmodium in order to prevent transmission are important components of malaria control programmes. Reducing gametocyte carriage is central to the control of Plasmodium falciparum transmission as infection can result in extended periods of gametocytaemia. Unfortunately the number of drugs with activity against gametocytes is limited. Primaquine is currently the only licensed drug with activity against the sexual stages of malaria parasites and its use is hampered by safety concerns. This shortcoming is likely the result of the technical challenges associated with gametocyte studies together with the focus of previous drug discovery campaigns on asexual parasite stages. However recent emphasis on malaria eradication has resulted in an upsurge of interest in identifying compounds with activity against gametocytes. This review examines the gametocytocidal properties of currently available drugs as well as those in the development pipeline and examines the prospects for discovery of new anti-gametocyte compounds.

Toxicology in the ICU: Part 2: specific toxins

This is the second of a three-part series that reviews the generalized care of poisoned patients in the ICU. This article focuses on specific agents grouped into categories, including analgesics, anticoagulants, cardiovascular drugs, dissociative agents, carbon monoxide, cyanide, methemoglobinemia, cholinergic agents, psychoactive medications, sedative-hypnotics, amphetamine-like drugs, toxic alcohols, and withdrawal states. The first article discussed the general approach to the toxicology patient, including laboratory testing; the third article will cover natural toxins.

Medications and glucose-6-phosphate dehydrogenase deficiency: an evidence-based review

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common human enzyme defect and one of the most common genetic disorders worldwide, with an estimated 400 million people worldwide carrying a mutation in the G6PD gene that causes deficiency of the enzyme. Although drug-induced haemolysis is considered the most common adverse clinical consequence of G6PD deficiency, significant confusion exists regarding which drugs can cause haemolytic anaemia in patients with G6PD deficiency. In the absence of consensus among physicians, patients are subject to conflicting advice, causing uncertainty and distress. In the current review we aimed, by thorough search of the medical literature, to collect evidence on which to base decisions either to prohibit or allow the use of various medications in patients with G6PD deficiency. A literature search was conducted during May 2009 for studies and case reports on medication use and G6PD deficiency using the following sources: MEDLINE (1966-May 2009), PubMed (1950-May 2009), the Cochrane database of systematic reviews (2009), and major pharmacology, internal medicine, haematology and paediatric textbooks. After assessing the literature, we divided medications into one of three groups: medications that should be avoided in individuals with G6PD deficiency, medications that were considered unsafe by at least one source, but according to our review can probably be given safely in normal therapeutic dosages to individuals with G6PD deficiency as evidence does not contravene their use, and medications where no evidence at all was found to contravene their use in G6PD-deficient patients. It is reasonable to conclude that, over time, many compounds have been wrongly cited as causing haemolysis because they were administered to patients experiencing an infection-related haemolytic episode. We found solid evidence to prohibit only seven currently used medications: dapsone, methylthioninium chloride (methylene blue), nitrofurantoin, phenazopyridine, primaquine, rasburicase and tolonium chloride (toluidine blue). Regarding all other medications, our review found no evidence to contravene their use in normal therapeutic doses to G6PD-deficient patients. There is a need for evidence-based global consensus regarding medication use in G6PD-deficient patients.

Dapsone-Associated Methaemoglobinaemia in Patients with a Haematologic Malignancy

Methaemoglobinaemia is an uncommon problem which can significantly impact on oxygen carriage and may necessitate intensive care management. The occurrence of symptomatic methaemoglobinaemia over a three-month period in four patients with haematological malignancies on dapsone for Pneumocystis jiroveci pneumonia prophylaxis prompted a review of its use in this group of patients. We performed a retrospective audit to identify any contributing factors. Co-oximetry was employed to identify patients with methaemoglobinaemia. Thirty-four patients with haematological malignancies received dapsone between January and December 2008, of whom 53% (n=18) had co-oximetry studies done. Raised methaemoglobin levels (≥1.5%) were seen in 13 patients, four of them symptomatic. Mean peak level was of 7.84% (range 1.9 to 26.8%). Eight patients required intensive care support. Mean onset of methaemoglobinaemia was 11.8 days (range 4 to 18 days) following dapsone commencement. All patients were anaemic with an average haemoglobin of 85.5 g/l (range 59 to 111 g/l). All patients were prescribed ‘azole’ antifungal agents and five patients were also on high-dose steroids, both agents known to induce cytochrome P-450 enzymes and hence potentiating dapsone toxicity. Our experience suggests that dapsone should be used with caution in patients with haematological malignancies as they are particularly at risk of developing symptomatic methaemoglobinaemia due to underlying anaemia, immunosuppression and potential drug interactions. The current recommendation of dapsone for Pneumocystis jiroveci pneumonia prophylaxis in this group of patients needs to be reviewed. When methaemoglobinaemia does occur, early recognition is possible with routine co-oximetry testing and prompt treatment may lessen the need for or duration of intensive care supports.

Severe hemolysis and methemoglobinemia following fava beans ingestion in glucose-6-phosphatase dehydrogenase deficiency: case report and literature review

INTRODUCTION

Reduced concentrations of glucose-6-phospate dehydrogenase (G6PD) render erythrocytes susceptible to hemolysis under conditions of oxidative stress. In favism, the ingestion of fava beans induces an oxidative stress to erythrocytes, leading to acute hemolysis.

DISCUSSION

The simultaneous occurrence of methemoglobinemia has been reported only scarcely, despite the fact that both phenomena are the consequence of a common pathophysiologic mechanism. The presence of methemoglobinemia has important diagnostic and therapeutic consequences. We report a previously healthy boy who presented with combined severe hemolytic anemia and cyanosis due to methemoglobinemia, following the ingestion of fava beans. His condition was complicated by the development of transient acute renal failure. A G6PD-deficiency was diagnosed. We review the literature on the combination of acute hemolysis and methemoglobinemia in favism. Pathophysiologic, diagnostic, and therapeutic aspects of this disorder are discussed.

Acute methaemoglobinaemia after massive nitrobenzene ingestion

Flower-N is a flowering stimulant composition with 22% nitrobenzene. The main systemic effect associated with human exposure to nitrobenzene is methaemoglobinaemia. A 25-year-old female presented after 3 hours following ingestion of 100 ml of 22% Nitrobenzene (Flower-N). Her initial methaemoglobin (MetHb) was 81%; this responded to methylene blue. However, she developed recurrent methaemoglobinaemia on days 3 and 5 with haemolytic anaemia. The treatments that were provided were repeated methylene blue treatment and exchange transfusion. Nitrobenzene ingestion is a known cause of methaemoglobinaemia and haemolytic anaemia. The recurrence suggests a long half-life. The recurrent MetHb has clinical implications as patients may require repeated treatment. Massive nitrobenzene ingestion can cause haemolysis and recurrent methaemoglobinaemia.

Severe methemoglobinemia linked to gel-type topical benzocaine use: a case report

BACKGROUND

Methemoglobinemia is an uncommon cause of tissue hypoxia, but it can be life threatening if it is not identified and treated promptly.

OBJECTIVES

To highlight the importance of understanding the potential risks of over-the-counter medications, especially in unsupervised use. Topical benzocaine must be used with caution, even in the healthy population.

CASE REPORT

We report a case of methemoglobinemia secondary to topical benzocaine gel. A 6-year-old boy presented to our Pediatric Emergency Department with cyanosis, vomiting, and lethargy after using a gel-type, 7.5% benzocaine (Baby Orajel) for a toothache. Physical examination revealed dusky blue skin, tachycardia, tachypnea, and a normal neurologic examination. His percutaneous oxygen saturation remained 77-83% despite the administration of 100% oxygen. His arterial blood sample had a dark chocolate color appearance, and methemoglobinemia was suspected. His methemoglobin level was 69.9%, which is considered a lethal level. After a single dose of methylene blue (1 mg/kg/dose), cyanosis was reduced and oxygenation improved.

CONCLUSION

Over-the-counter topical benzocaine should be used with caution, and the presence of methemoglobinemia must be promptly identified and treated.

The dilemma of approving antidotes

Clinical trials with antidotes are difficult to perform for a variety of practical, ethical, and financial reasons. As acute poisoning is a rare event, the commercial interest in basic and clinical research is low. Poisoned patients are usually not available for normal clinical trial procedures and, if they are, they cannot give informed consent. This situation results in a dilemma: antidotes are essential drugs. A resolution of the Council of Europe requests to guarantee the optimal availability of antidotes and the improvement of their use. As comprehensive data on the efficacy of antidotes are often missing, a marketing authorisation under exceptional circumstances according to Article 14(8) of Regulation (EC) No. 276/2004, will often be the only way to get an approval, as: (1) the indications for which the product in question is intended are encountered so rarely that the applicant cannot reasonably be expected to provide comprehensive evidence ("orphan drug"), (2) in the present state of scientific knowledge, comprehensive information cannot be provided, or (3) it would be contrary to generally accepted principles of medical ethics to collect such data. Typically, data on antidotes are obtained from a patchwork of studies with animals, human tissue and a few observations from human poisoning corroborated with data from clinical observations and biochemistry. Generalisations from chemical and mechanistic similarities between groups of poisons are usual, but often lack scientific evidence. Current standards of good clinical practice can rarely be observed. Therefore, public funding and other financial support are necessary incentives to initiate trials in this important area.