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Table of Contents
Year : 2014  |  Volume : 30  |  Issue : 1  |  Page : 86-88

Dapsone-induced methemoglobinemia: "Saturation gap"-The key to diagnosis

Department of Anesthesiology and Critical Care, Armed Forces Medical College, Pune, Maharashtra, India

Date of Web Publication24-Jan-2014

Correspondence Address:
Shivinder Singh
Department of Anesthesiology and Critical Care, Armed Forces Medical College, Solapur Road, Pune - 410040, Maharashtra
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0970-9185.125710

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Two cases of Acquired Methemoglobinemia are presented. The significance of a high index of suspicion for diagnosisis emphasized, especially in the presence of a "saturation gap". The various causes of acquired methemoglobinemia are enumerated and the management reviewed.

Keywords: Acquired methemoglobinemia, dapsone, saturation gap

How to cite this article:
Singh S, Sethi N, Pandith S, Ramesh GS. Dapsone-induced methemoglobinemia: "Saturation gap"-The key to diagnosis. J Anaesthesiol Clin Pharmacol 2014;30:86-8

How to cite this URL:
Singh S, Sethi N, Pandith S, Ramesh GS. Dapsone-induced methemoglobinemia: "Saturation gap"-The key to diagnosis. J Anaesthesiol Clin Pharmacol [serial online] 2014 [cited 2020 Aug 11];30:86-8. Available from:

  Introduction Top

Dapsone is a drug that is used in the treatment of leprosy and acne vulgaris owing to its immunosuppressive effects. Long-term administration of dapsone at standard doses (100 mg/day) results in methemoglobinemia in about 15% of patients. [1] Classically, low pulse oximeter readings are associated with hypoxia, however methemoglobinemia is an important albeit uncommon cause. [2] We report two cases of dapsone-induced methemoglobinemia with evident cyanosis, one in the emergency department and the other in a patient undergoing elective splenectomy.

  Case Report Top

Case 1

A 36-year-old woman was diagnosed with immune thrombocytopenic purpura in July 2012 and started on oral prednisolone and dapsone 100 mg/day. About 3 months later, she was admitted to the hospital with fatigue, headache, arthralgia, and severe dyspnea. Physical examination was normal except for peripheral cyanosis. She had a platelet count of 1,000/cmm, hemoglobin of 7.9 gm%. SpO 2 on room air was 84%, respiratory rate was 52/min. Owing to intolerance for non-invasive ventilation (NIV) and low saturation, the patient was intubated and ventilated.

Arterial blood gas (ABG) analysis revealed a pH of 7.43, PaO 2 -180 mmHg, PaCO 2 -32 mmHg, SaO 2 -99.1% on oxygen by facemask. In view of history of dapsone intake, cyanosis, low SpO 2 with normal PaO 2 and SaO 2 (on ABG) a diagnosis of methemoglobinemia was considered and dapsone was stopped, however, the facility for methemoglobin (methHb) estimation was not available. After 48 hrs of mechanical ventilation, she improved symptomatically and was extubated following a weaning trial. She was shifted to high dependency unit with oxygen 5l/min. The SpO 2 continued to remain low ranging from 88-92% over the next 3 days though the SaO 2 was normal. As the patient remained clinically stable, no further intervention was carried out and she made an uneventful recovery.

Case 2

An 8-year-old girl, a known case of immune thrombocytopenic purpura, with treatment history of oral prednisolone 20 mg/day and dapsone 50 mg/day since 1 year, was planned for laparoscopic splenectomy.

Pre-operative assessment revealed cushingoid features, skin discoloration all over the body and splenomegaly [Figure 1].
Figure 1: Cushingoid features with cyanosis

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She had a platelet count of 20,000/cmm but the other hematological variables were normal. Oxygen saturation on room air was 88%. During maintenance of general anesthesia with a 60:40 (nitrous oxide:oxygen) gas oxygen ratio, the SpO 2 rose to 92%. Vital signs, physical examination including bilateral air entry was normal, end tidal carbon dioxide and airway pressures were unremarkable. Intraoperative ABG analysis revealed a PaO 2 of 260 mmHg, pH 7.40, PaCO 2 38 mmHg, HCO 3 22.4 meq.l-1 and SaO 2 of 99%. Filter paper test done on the patient's blood comparing it with blood from a normal patient [Figure 2] which showed that the patient's blood remained dark even after exposure to atmospheric oxygen.
Figure 2: Filter paper test

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Deoxyhemoglobin can be distinguished from methHb by this simple bedside test. By placing 1 or 2 drops of the patient's blood on a white filter paper: Deoxyhemoglobin brightens after exposure to atmospheric oxygen, but methHb does not change color. [2]

She was transferred to the pediatric intensive care unit (ICU) with oxygen therapy by polymask at 5 l/min, as SpO 2 remained 86% on room air. Blood analysis showed methHb levels of 28.6%. Dapsone was stopped and the patient remained asymptomatic with supplemental oxygen by facemask. As the methHb levels were less than 30% and the patient was stable, therapy with methylene blue was not considered.

  Discussion Top

The majority of cases of acquired methemoglobinemia described in literature have resulted from exposure to exogenous oxidizing agents like nitrites used as preservatives in food or as a deliberate poison, [3],[4] amyl nitrate used as a recreational agent, [5],[6] abuse of paint thinner by addicts, [7] intake of nitrate containing vegetables [8] use of EMLA cream, [9],[10] and Dapsone intake. [11],[12]

The peak plasma concentrations of Dapsone are reached within 2-8 hours after ingestion. The mean elimination half-life varies from 10 to up to 80 hours in overdose situations. In healthy erythrocytes, cellular enzymes rapidly reduce any naturally occurring methHb. An exposure to oxidative medications can overcome these reducing enzymes thus causing an accumulation of methHb. [2] The role of nitric oxide (NO) in the pathophysiology of methemoglobinemia is also being studied. [13] The presence of methHb in the erythrocyte prevents the binding of oxygen as also increases the affinity of normal hemoglobin molecules for oxygen, shifting the oxygen dissociation curve to the left, thus further decreasing oxygen delivery to the tissues. [2],[14]

The symptoms and signs are proportional to the level of methemoglobin. Asymptomatic, if less than 15%; cyanosis in levels above15%; headache, dyspnea, nausea, tachycardia, and weakness in levels above 20%; coma sets in above 45%, and a high mortality rate is associated with levels above 70%. [15]

While cyanosis is a pointer to the diagnosis, varying oxygen saturation seen with pulse oximetry often confuses the issue. Standard colorimetric pulse oximeters show falsely low readings in mild toxicity and falsely high readings in severe toxicity by giving a constant reading in the low 80s in the presence of methHb. [2] On the other hand, most arterial blood gas analyzers calculate the oxygen saturation based on the PaO 2 (which is a measure of the dissolved oxygen in plasma) and so give false high values. Therefore, a "saturation gap" between the recorded saturation from the pulse oximeter as compared to the reported saturation in the arterial blood gas may be detected [16] and in the presence of a high index of suspicion, may be the key to diagnosis, especially in the resource limited setting. [3]

A pulse oximeter is now available that uses eight wavelengths of light and can accurately measure both methHb and carboxyhemoglobin (the Rainbow-SET Rad-57 Pulse CO-Oximeter, Masimo, Inc., Irvine, CA). It is capable of giving continuous readings of methHb level at the bedside. [17]

Management consists of removing the offending agent, high-dose oxygen, and intravenous methylene blue. Methylene blue (1-2−1 ) administered intravenously over a period of 3-5 minutes (contraindicated in G6PD deficiency) produces a rapid conversion of meth Hb to hemoglobin. Its use is recommended in all patients with meth Hb levels greater than 30% or in symptomatic patients at lower levels. Exchange transfusion and hyperbaric oxygen may also be considered for severe or refractory cases. [18]

These two cases emphasize the importance of good history taking, knowledge of drugs likely to cause methemoglobinemia and a high index of suspicion especially in the presence of a "saturation gap".

  References Top

1.Coleman MD, Rhodes LE, Scott AK, Verbov JL, Friedmann PS, Breckenridge AM, et al. The use of cimetidine to reduce dapsone-dependent methaemoglobinaemia in dermatitis herpetiformis patients. Br J Clin Pharmacol 1992;34:244-9.  Back to cited text no. 1
2.Steiner IP, Nichols DN. A case of dapsone-induced cyanosis in the emergency department. Isr J Emerg Med 2006;6:10-3.  Back to cited text no. 2
3.Nabukeera-Barungi N, Mworozi E. Sudden onset methaemoglobinaemia in a previously well Ugandan child: A case report and literature review. Pan Afr Med J 2012;11:49.  Back to cited text no. 3
4.Su YF, Lu LH, Hsu TH, Chang SL, Lin RT. Successful treatment of methemoglobinemia in an elderly couple with severe cyanosis: Two case reports J Med Case Rep 2012;6:290.  Back to cited text no. 4
5.Sheena Y, Baston EL, Downs A, Chester DL. A sticky situation: Methaemaglobinaemia in a hand trauma patient. BMJ Case Rep 20121;2012.  Back to cited text no. 5
6.Hall A, Stessel B, Bergmans D, Schnabel R. Two cases of acquired methemoglobinemia. Acta Anaesthesiol Belg 2012;63:97-100.  Back to cited text no. 6
7.Singh R, VinayagamS, Vajifdar H. Methemoglobinemia as a result of accidental lacquer thinner poisoning. Indian J Crit Care Med 2012;16:44-7.  Back to cited text no. 7
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8.Martinez A, Sanchez-Valverde F, Gil F, Clerigué N, Aznal E, Etayo V, et al. Methemoglobinemia induced by vegetable intake in infants in north Spain. J Pediatr Gastroenterol Nutr 2013;56:573-7.  Back to cited text no. 8
9.Schmitt C, Matulic M, Kervégant M, Tichadou L, Boutin A, Glaizal M, et al. Methaemoglobinaemia in a child treated with Emla(®) cream: Circumstances and consequences of overdose. Ann Dermatol Venereol 2012;139:824-7.  Back to cited text no. 9
10.García-Saura PL, Serrano Álvarez C. Methaemoglobinaemia in a healthy patient after using topical anaesthetic cream, for laser depilation. Rev Esp Anestesiol Reanim 2012.  Back to cited text no. 10
11.Ash-Bernal R, Wise R, Wright SM. Acquired methemoglobinemia: A retrospective series of 138 cases at 2 teaching hospitals. Medicine (Baltimore) 2004;83:265-73.  Back to cited text no. 11
12.Stichtenoth D. Lip cyanosis in dapsone therapy: Should the dosage be reduced? MMW Fortschr Med 2012;154:32.  Back to cited text no. 12
13.Sanyal T, Chakraborty S. Multiscale analysis of hypoxemia in methemoglobin anemia. Math Biosci 2013;241:167-80.  Back to cited text no. 13
14.Burke MD, DelGiacco E, Curran AL, Savior DC. Methhemoglobinemia in Besa EC eds. Emedicine Available from: http: //www. emedicine. com /Emerg/topic313. htm Updated: Jun 3, 2013 Accessed on 13 Dec 2013.  Back to cited text no. 14
15.Curry S. Methemoglobinemia. Ann Emerg Med 1982;11:214-21.  Back to cited text no. 15
16.Barker SJ, Tremper KK, Hyatt J. Effects of methemoglobinemia on pulse oximetry and mixed venous oximetry. Anesthesiology 1989;70:112-7.  Back to cited text no. 16
17.Annabi EH, Barker SJ. Severe methemoglobinemia detected by pulse oximetry. Anesth Analg 2009;108:898-9.  Back to cited text no. 17
18.Mycyk MB. Poisoning and drug overdosage. In: Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, Loscalzo J, Eds. Harrison's Online. 18 th ed. New York: McGraw-Hill; 2012.  Back to cited text no. 18


  [Figure 1], [Figure 2]

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