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

Anästhesie bei Patienten mit Glukose-6-Phosphat-Dehydrogenase-Mangel

Glucose-6-phosphate dehydrogenase (G6PD) deficiency, a frequent congenital human enzyme defect, is the most frequent cause of hemolytic anemia triggered by drugs or infectious diseases. Drugs which induce acute hemolysis in patients with G6PD deficiency are often used in anesthesia and perioperative pain therapy. Considering the fact that patients from geographic regions with a high prevalence of the disease are often treated in European hospitals, special attention should be paid to this problem. We report a case of a 30-year-old female patient with favism and review the disease and anesthesia-related implications.

Case studies in pediatric toxicology

Intentional and unintentional poisonings are encountered commonly in the pediatric population. Providers should be familiar both with the general approach to the poisoned child and with specific interventions required for certain toxic exposures.

Noninvasive in vivo monitoring of methemoglobin formation and reduction with broadband diffuse optical spectroscopy

We present noninvasive, quantitative in vivo measurements of methemoglobin formation and reduction in a rabbit model using broadband diffuse optical spectroscopy (DOS). Broadband DOS combines multifrequency frequency-domain photon migration (FDPM) with time-independent near infrared (NIR) spectroscopy to quantitatively measure bulk tissue absorption and scattering spectra between 600 nm and 1,000 nm. Tissue concentrations (denoted by brackets) of methemoglobin ([MetHb]), deoxyhemoglobin ([Hb-R]), and oxyhemoglobin ([HbO2]) were determined from absorption spectra acquired in "real time" during nitrite infusions in nine pathogen-free New Zealand White rabbits. As little as 30 nM [MetHb] changes were detected for levels of [MetHb] that ranged from 0.80 to 5.72 microM, representing 2.2 to 14.9% of the total hemoglobin content (%MetHb). These values agreed well with on-site ex vivo cooximetry data (r2= 0.902, P < 0.0001, n = 4). The reduction of MetHb to functional hemoglobins was also carried out with intravenous injections of methylene blue (MB). As little as 10 nM changes in [MB] were detectable at levels of up to 150 nM in tissue. Our results demonstrate, for the first time, the ability of broadband DOS to noninvasively quantify real-time changes in [MetHb] and four additional chromophore concentrations ([Hb-R], [HbO2], [H2O], and [MB]) despite significant overlapping spectral features. These techniques are expected to be useful in evaluating dynamics of drug delivery and therapeutic efficacy in blood chemistry, human, and preclinical animal models.

Occupational methaemoglobinaemia. Mechanisms of production, features, diagnosis and management including the use of methylene blue

Methaemoglobin is formed by oxidation of ferrous (FeII) haem to the ferric (FeIII) state and the mechanisms by which this occurs are complex. Most cases are due to one of three processes. Firstly, direct oxidation of ferrohaemoglobin, which involves the transfer of electrons from ferrous haem to the oxidising compound. This mechanism proceeds most readily in the absence of oxygen. Secondly, indirect oxidation, a process of co-oxidation which requires haemoglobin-bound oxygen and is involved, for example, in nitrite-induced methaemoglobinaemia. Thirdly, biotransformation of a chemical to an active intermediate that initiates methaemoglobin formation by a variety of mechanisms. This is the means by which most aromatic compounds, such as amino- and nitro-derivatives of benzene, produce methaemoglobin. Methaemoglobinaemia is an uncommon occupational occurrence. Aromatic compounds are responsible for most cases, their lipophilic nature and volatility facilitating absorption during dermal and inhalational exposure, the principal routes implicated in the workplace. Methaemoglobinaemia presents clinically with symptoms and signs of tissue hypoxia. Concentrations around 80% are life-threatening. Features of toxicity may develop over hours or even days when exposure, whether by inhalation or repeated skin contact, is to relatively low concentrations of inducing chemical(s). Not all features observed in patients with methaemoglobinaemia are due to methaemoglobin formation. For example, the intravascular haemolysis caused by oxidising chemicals such as chlorates poses more risk to life than the methaemoglobinaemia that such chemicals induce. If an occupational history is taken, the diagnosis of methaemoglobinaemia should be relatively straightforward. In addition, two clinical observations may help: firstly, the victim is often less unwell than one would expect from the severity of 'cyanosis' and, secondly, the 'cyanosis' is unresponsive to oxygen therapy. Pulse oximetry is unreliable in the presence of methaemoglobinaemia. Arterial blood gas analysis is mandatory in severe poisoning and reveals normal partial pressures of oxygen (pO2) and carbon dioxide (pCO2,), a normal 'calculated' haemoglobin oxygen saturation, an increased methaemoglobin concentration and possibly a metabolic acidosis. Following decontamination, high-flow oxygen should be given to maximise oxygen carriage by remaining ferrous haem. No controlled trial of the efficacy of methylene blue has been performed but clinical experience suggests that methylene blue can increase the rate of methaemoglobin conversion to haemoglobin some 6-fold. Patients with features and/or methaemoglobin concentrations of 30-50%, should be administered methylene blue 1-2 mg/kg/bodyweight intravenously (the dose depending on the severity of the features), whereas those with methaemoglobin concentrations exceeding 50% should be given methylene blue 2 mg/kg intravenously. Symptomatic improvement usually occurs within 30 minutes and a second dose of methylene blue will be required in only very severe cases or if there is evidence of ongoing methaemoglobin formation. Methylene blue is less effective or ineffective in the presence of glucose-6-phosphate dehydrogenase deficiency since its antidotal action is dependent on nicotinamide-adenine dinucleotide phosphate (NADP+). In addition, methylene blue is most effective in intact erythrocytes; efficacy is reduced in the presence of haemolysis. Moreover, in the presence of haemolysis, high dose methylene blue (20-30 mg/kg) can itself initiate methaemoglobin formation. Supplemental antioxidants such as ascorbic acid (vitamin C), N-acetylcysteine and tocopherol (vitamin E) have been used as adjuvants or alternatives to methylene blue with no confirmed benefit. Exchange transfusion may have a role in the management of severe haemolysis or in G-6-P-D deficiency associated with life-threatening methaemoglobinaemia where methylene blue is relatively contraindicated.

A severe methaemoglobinemia induced by nitrates: a case report

Methaemoglobinemia is a disorder in which the haemoglobin molecule is functionally altered and prevented from carrying oxygen. A variety of aetiologies including genetic, dietary, idiopathic and toxicological sources may cause methaemoglobinemia. Symptoms vary from mild headache to coma or death, and may not correlate with measured methaemoglobin concentrations. Patients with methaemoglobinemia appear deeply cyanotic, but are unresponsive to standard oxygen therapy. It is essential for the clinician to recognize the problem rapidly in patients without hypoxia by analysing their arterial blood gas. Methaemoglobin interferes with the accuracy of pulse oximetry. The antidote is methylene blue. We report a very unusual and dramatic case of methaemoglobinemia. A 23-year-old girl who arrived in the emergency department in a state of confusion with intense cyanosis. The night before she had drunk water with ice defiled by ammonium nitrate, poured from a broken pack of instant ice. The absence of improvement after the administration of oxygen and the 'chocolate brown' colour of the arterial blood gave us the most important clue in suspecting the diagnosis of methaemoglobinemia.

Severe methemoglobinemia after transesophageal echocardiography

Methemoglobinemia, an increased concentration of methemoglobin in the blood, is an altered state of hemoglobin whereby the ferrous form of iron is oxidized to the ferric state, rendering the heme moiety incapable of carrying oxygen. This can cause hypoxia, cyanosis, or even death. Severe methemoglobinemia resulting from oral benzocaine spray before endoscopic procedures has been reported as a rare complication. We report a case of severe acquired methemoglobinemia resulting from topical benzocaine use before transesophageal echocardiography. This case serves to highlight the severity of methemoglobinemia that can result from an otherwise innocuous agent even in small doses and the fact that prompt recognition and treatment of this disorder can be lifesaving.

Sodium thiosulfate fails to reduce nitrite-induced methemoglobinemia in vitro

OBJECTIVES

To determine whether sodium thiosulfate (STS) produces a clinically significant decline in sodium nitrite-induced methemoglobinemia in an in-vitro model.

METHODS

This was an in-vitro, controlled study where methemoglobinemia was induced by the addition of sodium nitrite (0.4 mg/mL) to 35-mL aliquots of blood obtained from ten healthy volunteers. Methemoglobin (MetHb) concentrations were measured at 5-minute intervals for 30 minutes by co-oximetry, and each aliquot was then subdivided into six 5-mL samples (time zero). Sample 1 served as control. The remaining samples received serial dilutions of STS (0.125 mg, 1.25 mg, 12.5 mg, 125 mg, 1,250 mg). MetHb concentrations were measured by co-oximetry at baseline, 0, 15, 30, 45, and 60 minutes. Areas under the MetHb concentration-time curve (AUC) between time zero and 60 minutes were compared using the Kruskal-Wallis test.

RESULTS

Methemoglobin concentrations increased from 0.07 g/dL (+/-0.06) at baseline to 8.42 g/dL (+/-0.69) at time 0 (the addition of STS). No significant difference was detected between baseline and time 0 hemoglobin concentrations (15.8 +/- 0.5 vs. 16.1 +/- 0.6 g/dL). There was no detectable difference found between the AUCs (measured in g min/dL) of any of the STS serial dilutions or control groups (0.125 mg STS = 576.01 +/- 42.53; 1.25 mg STS = 573.47 +/- 40.82; 12.5 mg STS = 583.68 +/- 42.29; 125 mg STS = 554.75 +/- 42.68; 1,250 mg STS = 566.95 +/- 38.08; p = 0.81).

CONCLUSIONS

Sodium thiosulfate was not found to be an effective reducing agent for the acute treatment of methemoglobinemia.

Treatment of high-risk, refractory acquired methemoglobinemia with automated red blood cell exchange

Ingestion of strong oxidant substances may result in acquired methemoglobinemia, a clinical condition in which the oxidized blood hemoglobin is incapable of delivering oxygen to the tissues, and the patient becomes cyanotic. Traditional first-line therapy consists of infusion of methylene blue, whose action depends on the availability of reduced nicotinamide adenine nucleotide phosphate (NADPH) within the red blood cell (RBC). Some patients, particularly those who are deficient in glucose-6-phosphate dehydrogenase (G6PD), will not benefit from methylene blue. In these patients, and in some patients who have ingested very strong oxidants, methylene blue may also precipitate Heinz body hemolytic anemia. We present a case of severe, acquired methemoglobinemia in a 26-month-old, 9.8-kg boy with G6PD deficiency. He was cyanotic, in respiratory failure, intubated in a pediatric intensive care unit. In typical fashion, he did not respond to methylene blue. Manual exchange of two whole blood volumes, performed over 4 1/2 hr, also failed to resolve his severe methemoglobinemia. An automated RBC exchange (1.3 RBC volume), lowered his methemoglobin content from 31.8% to 7% in a single 40-min procedure. Thereafter his methemoglobin level continued to decrease rapidly and spontaneously. He was discharged home 2 days later, with 0.4% methemoglobin. To our knowledge, this is the first report to demonstrate the (potentially superior) effectiveness of automated RBC exchange for treatment of patients with high-risk acquired methemoglobinemia, that is, those with G6PD deficiency or who have ingested strong oxidants.

Failure of intravenous N-acetylcysteine to reduce methemoglobin produced by sodium nitrite in human volunteers: A randomized controlled trial

STUDY OBJECTIVE

To determine whether intravenous N -acetylcysteine (NAC) produces a clinically significant decline in sodium nitrite-induced methemoglobinemia in human volunteers.

METHODS

We conducted a randomized, control crossover trial with each subject serving as his own control. Methemoglobinemia was induced with intravenous sodium nitrite (4 mg/kg) administered over 10 minutes starting at time 0. At time 30 minutes, subjects were randomly assigned to treatment with intravenous NAC for 100 minutes (150 mg/kg over 1 hour followed by 14 mg/kg per hour for 40 minutes) or administration of an equal volume of 5% dextrose in water. Each subject received the alternative treatment after an interval of at least 1 week. Blood methemoglobin concentrations were measured by multiwavelength co-oximetry at time 0, 15, 30, 50, 70, 90, 110, and 130 minutes. Area under the methemoglobin concentration-time curve (AUC) between 30 and 130 minutes was compared between groups using a 2-tailed, paired t test.

RESULTS

There were no statistically significant differences in the control and treatment groups with respect to baseline hemoglobin or methemoglobin concentrations, as well as nitrite-induced methemoglobin concentrations at the initiation of treatment (0.85+/-0.06 g/dL, 0.88+/-0.04 g/dL; mean+/-SEM; P =.31). Mean AUC for the control group (77.1+/-5.7 g x min/dL) was significantly lower than the mean AUC for the treatment group (84.5+/-4.7 g x min/dL); P =.01).

CONCLUSION

Intravenous NAC failed to enhance methemoglobin reduction in this model.

Utility of acetylcysteine in treating poisonings and adverse drug reactions

As recognition of the role of free radicals and reactive toxins in the pathogenesis of disease, poisoning, and adverse drug reactions has evolved, interest in the use of acetylcysteine as a modulator of these effects has steadily increased in recent years. Acetylcysteine is commonly thought to serve as a glutathione precursor and consequently can increase or sustain intracellular glutathione which scavenges reactive oxygen species caused by toxins or subsequent tissue injury. At least 10 additional mechanisms of action for acetylcysteine have been demonstrated in various laboratory models, but a unifying framework of its actions is still to be proposed. This paper reviews the current experimental and therapeutic status of acetylcysteine for the treatment of poisonings and adverse drug reactions. Of the 45 potential uses of acetylcysteine that were identified for the treatment of poisonings or adverse drug reactions, 14 of the toxic effects have little support for its use while promising results have been demonstrated for 27 toxicities. Currently, treatment of acute paracetamol (acetaminophen) poisoning is the only widely accepted clinical indication for acetylcysteine as a treatment for poisoning or adverse drug reactions. In many clinical situations acetylcysteine is used empirically utilising modifications of dosage regimens employed for paracetamol poisoning. Often it is difficult to determine the benefit of therapy with acetylcysteine owing to the nature of the toxicity being treated, the use of other therapies, the presence of comorbid conditions, and the small number of patients studied. The diverse and positive nature of the investigations suggest that there is considerable promise in acetylcysteine as a research tool and pharmacological agent.

Methemoglobinemia: etiology, pharmacology, and clinical management

Methemoglobin (MHb) may arise from a variety of etiologies including genetic, dietary, idiopathic, and toxicologic sources. Symptoms vary from mild headache to coma/death and may not correlate with measured MHb concentrations. Toxin-induced MHb may be complicated by the drug's effect on other organ systems such as the liver or lungs. The existence of underlying heart, lung, or blood disease may exacerbate the toxicity of MHb. The diagnosis may be complicated by the effect of MHb on arterial blood gas and pulse oximeter oxygen saturation results. In addition, other dyshemoglobins may be confused with MHb. Treatment with methylene blue can be complicated by the presence of underlying enzyme deficiencies, including glucose-6-phosphate dehydrogenase deficiency. Experimental antidotes for MHb may provide alternative treatments in the future, but require further study.

Methemoglobinemia secondary to topical silver nitrate therapy--a case report

Methemoglobinemia is a rare complication in individuals exposed to nitrates or nitrites. Whereas methemoglobinemia is a recognized potential complication in burn patients treated with topical 0.5% silver nitrate solution, no report of methemoglobinemia in burn patients has been present in the literature for more than 15 years. We raise consciousness about this complication with a case report of a 12-month-old child with necrotizing fasciitis resulting from a cutaneous flank infection. The patient developed cyanosis 20 days after initiation of topical treatment with 0.5% silver nitrate solution. Intravenous injection of methylene blue can restore normal blood oxygenation.

Lessons to be learned: a case study approach: prolonged methaemoglobinaemia due to inadvertent dapsone poisoning; treatment with methylene blue and exchange transfusion

The authors present a case of methaemoglobinaemia of acute onset, with an unusually protracted course. The long persistence of this disorder led to a search for the cause which was eventually traced to medication with dapsone. The latter was found to be inappropriately being taken by the patient instead of an antispasmodic that had been prescribed for a spinal condition; this was because the tablets had been incorrectly labelled and dispensed in a pharmacy. The patient took increasing doses of the presumed 'antispasmodic' tablets as they seemed to lack clinical effect, thus further exacerbating the toxic consequences. Moreover, the patient brought his wrongly labelled tablets into hospital and was allowed to use them there, contrary to normal hospital policy. As treatment for the methaemoglobinaemia both bolus and continuous infusions of methylene blue were used, which probably contributed to the severe haemolysis which followed. Furthermore, the development of a rare side effect of dapsone toxicity, namely that of a sensorimotor neuropathy, is reported.

Methemoglobinemia induced by methylene blue pertubation during laparoscopy

Methylene blue is used to check tubal patency during laparoscopy. A case of methemoglobinemia which was induced by methylene blue is presented. Methemoglobinemia is usually treated with methylene blue; however, in patients with glucose-6-phosphate dehydrogenase deficiency, methylene blue can induce methemoglobinemia.

N-acetylcysteine reduces methemoglobin in an in-vitro model of glucose-6-phosphate dehydrogenase deficiency

OBJECTIVE

To determine whether N-acetylcysteine (NAC) reduces methemoglobin (MHB) in an in-vitro model of glucose-6-phosphate dehydrogenase (G6PD) deficiency, given that methylene blue is an ineffective MHB antidote in G6PD deficiency.

METHODS

Five volunteers donated blood, which was divided equally into 2 test tubes, centrifuged, and washed with Tris-Mopps buffer (pH 7.4, 15 mmol/L glucose). Both tubes were incubated with epiandrosterone (EA) (400 micromol), a specific inhibitor of G6PD. After 75 microL of 0.18 mol hydroxylamine (HA) was added to induce MHB formation, 150 microL of NAC (20 mg/mL) was added to tube 1 and 150 microL of phosphate-buffered saline (PBS) was added to tube 2 as a volume control. Serial MHB levels are reported as a percentage of total hemoglobin (Hb). G6PD activity was measured at baseline, 15 minutes after EA, and at 5 hours.

RESULTS

Mean G6PD activity at baseline was 9.2+/-2.9 U/g Hb (normal >4.6 U/g Hb); 15 minutes after EA was 3.0+/-1.0 U/g Hb; and at experiment's end was 2.3+/-0.7 U/g Hb. The mean (+/-SD) areas under the concentration-time curves (AUCs) of NAC-EA-HA and PBS-EA-HA samples were compared using an unpaired t-test and were significantly different: PBS-EA-HA, 20,400+/-1,100 % min, vs NAC-EA-HA, 10,400+/-1,000 % min, respectively (p < 0.05).

CONCLUSION

In this in-vitro model of G6PD deficiency, NAC efficiently reduced MHB.

Chronic methemoglobinemia: improving hemoglobin saturation monitoring during anesthesia

Methemoglobin interferes with the accuracy of pulse oximetry data. Methemoglobinemia is caused by many factors, both congenital and acquired. However, the increasing usage of dapsone, which converts hemoglobin to methemoglobin, is increasing the number of patients with methemoglobinemia. We present the case of a patient with dapsone-induced methemoglobinemia who was successfully treated with methylene blue, which converts methemoglobin back to hemoglobin.

Dapsone intoxication: two case reports

Two patients with dapsone intoxication, an adult and a 16-month-old child, are reported. Both developed symptomatic methemoglobin concentrations, of 35% and 37%, respectively, and improved with intravenous methylene blue. Methemoglobin levels subsequently rose in both cases to 25% at 24 and 37 hours, respectively. The recurrence of elevated methemoglobin levels resulted from either continued absorption of dapsone or its toxic metabolite from the gastrointestinal tract. Both patients were begun on serial oral activated charcoal and the child received a second methylene blue treatment. During the intoxication, serum hemoglobin concentrations dropped 2 gm with an increase in the reticulocyte count. Review of 20 cases of dapsone overdose from the literature showed that the major toxic manifestations are methemoglobinemia and hemolysis. Delayed sulfhemoglobinemia, reported in only one case, resolved spontaneously. The treatment of dapsone intoxication is intravenous methylene blue for symptomatic methemoglobinemia, gastric decontamination, and early administration of serial oral activated charcoal. Hemolysis is mild but transfusions may be required for patients with a glucose-6-phosphate dehydrogenase deficiency.

Poisonings in laboratory personnel and health care professionals

A case report of an unresponsive chemist presenting to the emergency department is presented; in retrospect, the patient was discovered to have intentionally ingested cyanide. A review of literature regarding ingestions in laboratory and health care personnel reveals five common points encountered in these personnel: barbiturates, carbon monoxide, cyanide, azides, and methemoglobin-inducing chemicals. Key diagnostic findings, in the absence of history of exposure, are discussed for these five agents.

Management of dapsone poisoning complicated by methaemoglobinaemia

The currently recommended dosage regimen for methylene blue (intermittent bolus dose) in the treatment of methaemoglobinaemia caused by dapsone is often inadequate. This is due to the long half-life of dapsone which provides a continuing oxidative stress that can cause a recurrence of clinically significant methaemoglobinaemia. Methylene blue infusion is effective, as demonstrated in an illustrative case report, and should be supported by repeated doses of activated charcoal to enhance dapsone elimination. The principles of treatment of methaemoglobinaemia due to dapsone can be applied to methaemoglobinaemia due to any agent producing prolonged oxidative stress.

Organic nitrate-induced methemoglobinemia

Metabolism of organic nitrates results in the formation of inorganic nitrites that can oxidize hemoglobin to methemoglobin. Clinical trials have investigated the risk of developing methemoglobinemia during the therapeutic use of organic nitrates. Based on the results of these trials, organic nitrate use does appear to increase methemoglobin content but not to a clinically significant extent. These elevations may be related to dose but study design prevents determination of any dose-response relationship. Despite these results, several case reports of patients experiencing clinically significant methemoglobinemia can be found in the literature. These patients generally received organic nitrates at doses greater than those used in the clinical trials, and several were diagnosed early during coronary surgery. Renal dysfunction and concurrent use of methemoglobin inducers may be contributing factors. Patients receiving organic nitrates should be monitored for symptoms suggestive of methemoglobinemia, especially while receiving large doses. Treatment of nitrate-induced methemoglobinemia consists of discontinuing the medication and, when necessary, administering methylene blue.

Treatment of aniline poisoning with exchange transfusion

A case of aniline poisoning with methemoglobinemia unresponsive to methylene blue is described. Exchange transfusion proved successful. A rationale for the failure of methylene blue under these circumstances is described.

Anaesthesia and glucose-6-phosphate dehydrogenase deficiency. A case report and review of the literature

Anaesthetic management of a patient with glucose-6-phosphate dehydrogenase deficiency is described. The pathogenesis and various complications relating to this common hereditary blood disorder are reviewed. Problems related to anaesthesia in the presence of glucose-6-phosphate dehydrogenase deficiency are discussed.

Intraoperative cyanosis: a case of dapsone-induced methaemoglobinaemia

Intraoperative cyanosis is most commonly caused by hypoxaemia. The anaesthetist is required to perform a rapid series of diagnostic manoeuvres and take remedial action. Occasionally methaemoglobin, sulfhaemoglobin, or haemoglobin M, undetected preoperatively, is the cause of the cyanosis. We report a case of methaemoglobinaemia secondary to dapsone ingestion that was diagnosed intraoperatively. Dapsone, a sulfone, is used therapeutically to treat leprosy and dermatitis herpetiformis. The differential diagnosis of cyanosis, and the origin and fate of methaemoglobin are discussed. In addition the diagnostic steps and the laboratory investigations required to make the diagnosis are listed.

Drug- and chemical-induced methaemoglobinaemia. Clinical features and management

Methaemoglobin is haemoglobin with the iron oxidised to the ferric (Fe ) state from the normal (or reduced) ferrous (Fe++) state. Methaemoglobinaemia refers to the presence of greater than the normal physiological concentration of 1 to 2% methaemoglobin in erythrocytes. Methaemoglobin is incapable of transporting oxygen. It has an intense dark blue colour; thus, clinical cyanosis becomes apparent at a concentration of about 15%. The symptoms are manifestations of hypoxaemia with increasing concentrations of methaemoglobin. Concentrations in excess of 70% are rare, but are associated with a high incidence of mortality. Methaemoglobinaemia may be congenital but is most often acquired. Congenital methaemoglobinaemia is of two types. The first is haemoglobin M disease (several variants) which is due to the presence of amino acid substitutions in either the alpha or beta chains. The second type is due to a deficiency of the NADH-dependent methaemoglobin reductase enzyme. This deficiency has an autosomal dominant transmission, and both homozygous and heterozygous forms have been reported. The heterozygous form is not normally associated with clinical cyanosis, but such individuals are more susceptible to form methaemoglobin when exposed to inducing agents. A wide variety of chemicals including several drugs, e.g. the antimalarials chloroquine and primaquine, local anaesthetics such as lignocaine, benzocaine and prilocaine, glyceryl trinitrate, sulphonamides and phenacetin, have been reported to induce methaemoglobinaemia. An intense 'chocolate brown' coloured blood and central cyanosis unresponsive to the administration of 100% oxygen suggests the diagnosis. A simple bedside test using a drop of the patient's blood on filter paper helps to confirm the clinical suspicion. Methaemoglobin can be quantitated rapidly by a spectrophotometric method.(ABSTRACT TRUNCATED AT 250 WORDS)

Methemoglobinemia

Oxygen transport, the major function of hemoglobin, is dependent upon reduced heme iron. In the red cell, the heme iron is maintained in the reduced form by the methemoglobin reduction system. When the balance between oxidation and reduction of heme iron is perturbed due to the presence of excessive oxidants, decreased reducing capacity or the presence of abnormal hemoglobin, methemoglobinemia ensues. In most cases methemoglobinemia is transitory and of no major clinical consequence. Occasionally, however, it can be life threatening and must be rapidly diagnosed and treated. When methemoglobinemia is of hereditary nature, either due to deficiency of red cell NADH-methemoglobin reductase or due to the presence of M hemoglobin, it is a lifelong problem. Since most of these patients do not have major disabling symptoms, the treatment is aimed at correction of cyanosis.

An infant with sepsis and methemoglobinemia

A 3-week-old child arrived at the emergency room with the concurrent onset of sepsis and methemoglobinemia associated with diarrhea. Subsequently, the child had two recurrent episodes of methemoglobinemia with re-exacerbations of his diarrhea. Possible causes and associations of methemoglobinemia are presented: particular emphasis is placed on the early recognition and rapid diagnosis of this life-threatening condition.

Studies of the efficacy and potential hazards of methylene blue therapy in aniline-induced methaemoglobinaemia

The similarity between poison and antidote was known to the ancient Greeks who used the same word, pharmakon, for both. This paper presents evidence that aniline (the toxin) and methylene blue (ther therapy) are in fact remarkably similar and additive in some of their effects on erythrocytes. Studies were prompted by a case of aniline-induced methaemoglobinaemia in which two injections of methylene blue did not rapidly eliminate cyanosis and were followed by severe, delayed haemolysis. Interactions between aniline and methylene blue were studied in cats which, although showing important differences from man in their haemoglobin and splenic vasculature, represent a useful model. Methylene blue potentiated the oxidative denaturation of haemoglobin by aniline as judged by the size and number of Heinz bodies and their turbidity in haemolysate. It also aggravated and prolonged the fall in erythrocyte reduced glutathione content which occurred at a time of maximum Heinz body production. While methylene blue in judicious dosage will reduce the content of methaemoglobin after aniline exposure, it may not eliminate visible cyanosis. Repeated injections of methylene blue can markedly aggravate subsequent haemolysis without further lowering methaemoglobin content.

Methemoglobinemia

Methemoglobinemia must be considered in the differential diagnosis of the cyanotic patient. Methemoglobin cannot carry oxygen or carbon dioxide. Methemoglobinemia can result from exposure to a wide variety of chemicals, including many commonly prescribed drugs, usually in an overdose situation. Most cases require only supportive therapy and assessment for other toxic complications. Severe cases may result in hypoxia and require treatment with methylene blue. Not all cases respond to methylene blue, and methylene blue itself may produce serious side effects.

Acquired methemoglobinemia and hemolytic anemia after usual doses of phenazopyridine

Two patients developed symptomatic methemoglobinemia and hemolytic anemia after treatment with phenazopyridine. Methemoglobinemia appears to be a rare occurrence after commonly used doses of phenazopyridine; phenazopyridine-associated hemolytic anemia has been reported both after overdose and after usual doses. The presentation of methemoglobinemia in the first patient and the response to treatment with methylene blue in the second patient were unusual, suggesting that the patients had a red cell defect or were exposed to other oxidizing substances. One of the major metabolites of phenazopyridine is aniline, a known cause of methemoglobinemia. Aniline-induced methemoglobinemia is less responsive to treatment with methylene blue than nitrate- or nitrite-induced methemoglobinemia. This may explain, in part, the poor response to methylene blue by one of our patients.

Methemoglobinemia from isobutyl nitrite preparations

Ingestion of preparations containing isobutyl nitrite can lead to rapidly fatal methemoglobinemia. We report the cases of three patients presenting with methemoglobinemia secondary to ingestion or inhaling the contents of an over-the-counter room odorizer preparation containing isobutyl nitrite. The condition was treated successfully with administration of intravenous methylene blue.

Symptomatic methemoglobinemia with a commonly used topical anesthetic, cetacaine

Severe cyanosis resulting from acquired methemoglobinemia after application of a topical anesthetic, Cetacaine spray, occurred in a 37-year-old patient following bronchoscopy for postoperative atelectasis. Response to methylene blue therapy was dramatic and complete. Attention is drawn to a dangerous adverse effect of this commonly used topical anesthetic agent.

Mechanism of methaemoglobin reduction by human erythrocytes

The time course of methaemoglobin reduction in human erythrocytes treated with nitrite was studied at pH 7.4, 37 degrees C, in the presence or absence of Methylene Blue, and the changes in methaemoglobin, intermediate haemoglobins and oxyhaemoglobin during the reaction were analysed by isoelectric-focusing on Ampholine/polyacrylamide-gel plates. In both cases, with or without the dye, the intermediate haemoglobins were found to be present at (alpha 3+beta 2+)2 and (alpha 2+beta 3+)2 valency hybrids from their characteristic position on electrophoresis, but amounts changed consecutively with time. The amount of (alpha 3+beta 2+)2 was always greater than that of the (alpha 2+beta 3+)2 valency hybrid. This result is explained by the differences in redox potentials between alpha- and beta-chains in methaemoglobin tetramer. It was concluded that methaemoglobin was reduced in human erythrocytes through these two different pats: methaemoglobin leads to k+3 (alpha 2+beta 3+)2 leads to k+3 oxyhaemoglobin. The reaction rate constants k'"1 (= k+1+k+3) and k'+2(=k+2+k+4) were estimated from the changes in each component methaemoglobin, intermediate haemoglobins [(alpha 3+beta 2+)2+(alpha 2+beta 3+)2] and oxyhaemoglobin.