Methylene blue unresponsive methemoglobinemia

Methemoglobinemia Secondary to a Traditional Healing Practice Using Mothballs: A Need of Pediatric Vigilance

Acute-onset unexplained hypoxemia persisting despite 100% oxygen has a limited differential diagnosis but poses a challenging diagnostic dilemma. Methemoglobinemia, a hemolytic condition, may lead to significant complications if it goes undiagnosed during the critical golden hour of an emergency department (ED) presentation. This case report presents the clinical details of a 30-month-old child with acute intravascular hemolysis evident by severe pallor and hemoglobinuria and severe hypoxia documented on pulse oximetry. During the ABCDE (Airway, Breathing, Circulation, Disability, Exposure) of the primary survey, "exposure" revealed the parent's deliberate fastening of a mothball around the waist of the baby on the advice of a traditional healer, which was identified as the source of naphthalene toxicity. The swift intervention was undertaken for hypoxic respiratory compromise with 100% oxygen just after triage, and the naphthalene ball with the tied cloth was removed. Arterial blood gas and co-oximetry analysis confirmed the diagnosis of methemoglobinemia, and other laboratory tests suggested severe hemolytic anaemia as well as hemoglobinuria favouring intravascular hemolysis. With the exclusion of other common differentials for hemolytic anaemia, including sickle cell crisis, autoimmune hemolytic anaemia, hemolytic uremic syndrome, and G6PD deficiency, naphthalene exposure was considered the culprit for both hemolysis and methemoglobinemia. After obtaining the history of another similar episode of anaemia six months ago requiring blood transfusion, we retrospected on similar mothball exposure, but parents denied that, saying they were using the mothball only for the last 10 days on the advice of a local healer with intent to get rid of some evil power and sickness in their child. After analyzing the old records of prior hospitalization and getting assured of a normal report of G6PD level, intravenous methylene blue was administered. But in view of an inadequate response, a single blood volume exchange transfusion was performed during the ED stay only, which resulted in a notable reduction in subsequent methemoglobin levels and an improvement of the child's clinical condition by the second day. The child was discharged by the third day with no distress and no further episodes of hemoglobinuria, with detailed parental counselling and follow-up advice. This case underscores the imperative need for timely recognition and effective management of methemoglobinemia in the paediatric population while emphasizing the potential hazards associated with naphthalene exposure. Further comprehensive investigations are warranted to elucidate optimal treatment strategies and explore long-term outcomes in similar clinical scenarios.

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.

Identification of broad anti-coronavirus chemical agents for repurposing against SARS-CoV-2 and variants of concern

Endemic human coronaviruses (hCoVs) 229E and OC43 cause respiratory disease with recurrent infections, while severe acute respiratory syndrome (SARS)-CoV-2 spreads across the world with impact on health and societies. Here, we report an image-based multicycle infection procedure with α-coronavirus hCoV-229E-eGFP in an arrayed chemical library screen of 5440 clinical and preclinical compounds. Toxicity counter selection and challenge with the β-coronaviruses OC43 and SARS-CoV-2 in tissue culture and human airway epithelial explant cultures (HAEEC) identified four FDA-approved compounds with oral availability. Methylene blue (MB, used for the treatment of methemoglobinemia), Mycophenolic acid (MPA, used in organ transplantation) and the anti-fungal agent Posaconazole (POS) had the broadest anti-CoV spectrum. They inhibited the shedding of SARS-CoV-2 and variants-of-concern (alpha, beta, gamma, delta) from HAEEC in either pre- or post exposure regimens at clinically relevant concentrations. Co-treatment of cultured cells with MB and the FDA-approved SARS-CoV-2 RNA-polymerase inhibitor Remdesivir reduced the effective anti-viral concentrations of MB by 2-fold, and Remdesivir by 4 to 10-fold, indicated by BLISS independence synergy modelling. Neither MB, nor MPA, nor POS affected the cell delivery of SARS-CoV-2 or OC43 (+)sense RNA, but blocked subsequent viral RNA accumulation in cells. Unlike Remdesivir, MB, MPA or POS did not reduce the release of viral RNA in post exposure regimen, thus indicating infection inhibition at a post-replicating step as well. In summary, the data emphasize the power of unbiased, full cycle compound screens to identify and repurpose broadly acting drugs against coronaviruses.

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.

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.

Evidence for in vitro and in vivo activity of the antimalarial pyronaridine against Schistosoma

Background

Schistosomiasis is highly prevalent in Africa. Praziquantel is effective against adult schistosomes but leaves prepatent stages unaffected—which is a limit to patient management and elimination. Given the large-scale use of praziquantel, development of drug resistance by Schistosoma is feared. Antimalarials are promising drugs for alternative treatment strategies of Schistosoma infections. Development of drugs with activity against both malaria and schistosomiasis is particularly appealing as schistosome infections often occur concomitantly with malaria parasites in sub-Saharan Africa. Therefore, antiplasmodial compounds were progressively tested against Schistosoma in vitro, in mice, and in a clinical study.

Results

Amongst 16 drugs and 1 control tested, pyronaridine, methylene blue and 5 other antimalarials were highly active in vitro against larval stage schistosomula with a 50% inhibitory concentration below 10 μM. Both drugs were lethal to ex vivo adult worms tested at 30 μM with methylene blue also active at 10 μM. Pyronaridine treatment of mice infected with S. mansoni at the prepatent stage reduced worm burden by 82% and cured 7 out of 12 animals, however in mice adult stages remained viable. In contrast, methylene blue inhibited adult worms by 60% but cure was not achieved. In an observational pilot trial in Gabon in children, the antimalarial drug combination pyronaridine-artesunate (Pyramax) reduced S. haematobium egg excretion from 10/10 ml urine to 0/10 ml urine, and 3 out of 4 children were cured.

Conclusion

Pyronaridine and methylene blue warrant further investigation as candidates for schistosomiasis treatment. Both compounds are approved for human use and evidence for their potential as antischistosomal compounds can be obtained directly from clinical testing. Particularly, pyronaridine-artesunate, already available as an antimalarial drug, calls for further clinical evaluation.

Trial registration

ClinicalTrials.gov Identifier NCT03201770.

Praziquantel is still the only drug in use for the treatment of all Schistosoma spp. and is exclusively active against the adult life cycle stage, since schistosomes in the prepatent period of up to eight weeks are not affected by the drug. Although resistance to praziquantel has not been confirmed and its existence remains controversial, some countries have identified clinical schistosome isolates with reduced sensitivity to praziquantel, after deployment in mass drug administration programs. The need for a new antischistosomal compound is urgent, ideally exhibiting broad activity against all stages of the parasite’s life cycle present in humans. After testing a series of antiplasmodial compounds, the authors found that several compounds also exhibited antischistosomal activity at various life cycle stages of the worms, including pyronaridine and methylene blue, both compounds already approved for human use. A pilot trial with pyronaridine-artesunate done in Gabon showed the first promising results against Schistosoma infections.

In Vivo Transcutaneous Monitoring of Hemoglobin Derivatives Using a Red-Green-Blue Camera-Based Spectral Imaging Technique

Cyanosis is a pathological condition that is characterized by a bluish discoloration of the skin or mucous membranes. It may result from a number of medical conditions, including disorders of the respiratory system and central nervous system, cardiovascular diseases, peripheral vascular diseases, deep vein thrombosis, and regional ischemia. Cyanosis can also be elicited from methemoglobin. Therefore, a simple, rapid, and simultaneous monitoring of changes in oxygenated hemoglobin and deoxygenated hemoglobin is useful for protective strategies against organ ischemic injury. We previously developed a red-green-blue camera-based spectral imaging method for the measurements of melanin concentration, oxygenated hemoglobin concentration (C_HbO), deoxygenated hemoglobin concentration (C_HbR), total hemoglobin concentration (C_HbT) and tissue oxygen saturation (StO₂) in skin tissues. We leveraged this approach in this study and extended it to the simultaneous quantifications of methemoglobin concentration (C_metHb), C_HbO, C_HbR, and StO₂. The aim of the study was to confirm the feasibility of the method to monitor C_metHb, C_HbO, C_HbR, C_HbT, and StO₂. We performed in vivo experiments using rat dorsal skin during methemoglobinemia induced by the administration of sodium nitrite (NaNO₂) and changing the fraction of inspired oxygen (FiO₂), including normoxia, hypoxia, and anoxia. Spectral diffuse reflectance images were estimated from an RGB image by the Wiener estimation method. Multiple regression analysis based on Monte Carlo simulations of light transport was used to estimate C_HbO, C_HbR, C_metHb, C_HbT, and StO₂. C_metHb rapidly increased with a half-maximum time of less than 30 min and reached maximal values nearly 60 min after the administration of NaNO₂, whereas StO₂ dramatically dropped after the administration of NaNO₂, indicating the temporary production of methemoglobin and severe hypoxemia during methemoglobinemia. Time courses of C_HbT and StO₂, while changing the FiO₂, coincided with well-known physiological responses to hyperoxia, normoxia, and hypoxia. The results indicated the potential of this method to evaluate changes in skin hemodynamics due to loss of tissue viability and vitality.

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.

Methemoglobinemia in a 14-year-old girl with new-onset dyspnea

Methemoglobinemia is a rare and potentially life-threatening medical emergency that can be overlooked when evaluating a patient in respiratory distress. Without early recognition, patients may develop respiratory failure and die. This article describes a teenager who presented to the ED for dyspnea and lightheadedness and failed to respond to supplemental oxygen. She was eventually diagnosed with methemoglobinemia.

On the dysfunctional hemoglobins and cyanosis connection: practical implications for the clinical detection and differentiation of methemoglobinemia and sulfhemoglobinemia

Methemoglobinemia and sulfhemoglobinemia are potentially life-threatening blood-related disorders characterized by similar symptoms and markedly distinct treatment procedures. In this paper, we investigate the causal relationship between these conditions and the onset of cyanosis, which is typically associated with a purple or bluish skin coloration. More specifically, we perform controlled experiments to elicit cyanotic appearances resulting from different severity levels of these disorders and varying physiological conditions. We note that such experiments cannot be induced in living subjects without posing risks to their health. Accordingly, we have resorted to an in silico experimental approach supported by biophysical data reported in the literature. Besides bringing new insights about cyanotic chromatic variations elicited by methemoglobinemia and sulfhemoglobinemia, our investigation provides the basis for the proposition of a cost-effective protocol for the noninvasive detection and differentiation of these disorders. Our experimental results indicate that its sensitivity range is wider than what is provided by similar protocols employed in these tasks. Moreover, it has lower operational requirements than laboratory tests ordered to enable the diagnosis of these conditions. We believe that these aspects make the proposed protocol particularly suitable for deployment at the point of care of medical settings with limited access to laboratory resources.

Role of Automated Therapeutic Red Cell Exchange in the Setting of Acute Methemoglobinemia: Our Experience

Methemoglobinemia, an altered state of hemoglobin resulting in impaired oxygen delivery to the tissues can be congenital or following exposure/ingestion of various oxidant drugs or toxins. One of the earliest signs of methemoglobinemia is generalized cyanosis not improved on oxygen supplementation and presence of normal PO₂ on acid blood-gas analysis. Here, we report two cases of acquired methemoglobinemia following poisoning and our experience of managing them with automated therapeutic red cell exchange.

Noninvasive photoacoustic microscopy of methemoglobin in vivo

Due to the various causes of methemoglobinemia and its potential to be confused with other diseases, in vivo measurements of methemoglobin have significant applications in the clinic. Using photoacoustic microscopy (PAM), we quantified the average and the distributed percentage of methemoglobin both in vitro and in vivo. Based on the absorption spectra of methemoglobin, oxyhemoglobin, and deoxyhemoglobin, three wavelengths were chosen to differentiate methemoglobin from the others. The methemoglobin concentrations calculated from the photoacoustic signals agreed well with the preset concentrations. Then we imaged the methemoglobin percentage in microtubes that mimicked blood vessels. Average percentages calculated for five samples with different methemoglobin concentrations also agreed well with the preset values. Finally, we demonstrated the ability of PAM to detect methemoglobin in vivo in a mouse ear. Our results show that PAM can quantitatively image methemoglobin distribution in vivo.