Dapsone-Induced Methemoglobinemia after Hematopoietic Stem Cell Transplantation

Safe and Effective Prophylaxis with Bimonthly Intravenous Pentamidine in the Pediatric Hematopoietic Stem Cell Transplant Population

BACKGROUND

Without prophylaxis, Pneumocystis jiroveci pneumonia (PCP) develops in 5%-15% of pediatric hematopoietic stem cell transplant (HCT) patients with mortality above 50%. Trimethoprim-sulfamethoxazole is a standard PCP prophylaxis; pentamidine is frequently used as second-line prophylaxis because of trimethoprim-sulfamethoxazole's potential for cytopenias. Monthly intravenous (IV) pentamidine has variable efficacy with PCP infection rates of 0%-10% in pediatric patients, and higher breakthrough rates in those younger than 2 years. We hypothesized that bimonthly (twice monthly) pentamidine might have equivalent safety and improved efficacy; therefore, we conducted a retrospective analysis of bimonthly pentamidine PCP prophylaxis.

METHODS

We retrospectively reviewed records of all pediatric HCT patients who received bimonthly IV pentamidine between December 2006 and June 2013, and collected data regarding demographics, clinical course, prophylaxis rationale, laboratory values and adverse events.

RESULTS

Between December 2006 and June 2013, 111 pediatric HCT patients received bimonthly IV pentamidine (574 doses, 8758 patient-days); 31 patients were younger than 2 years at initiation. In the majority (53% of courses), pentamidine was initiated because of cytopenias. Fourteen patients (12.6% of patients, 2.4% of doses) experienced a side-effect prompting discontinuation, including 3 patients with infusion-related hypotension/anaphylaxis and 3 with acute pancreatic dysfunction. No patients [0% (95% confidence interval: 0-3.2)] developed PCP during or after bimonthly IV pentamidine prophylaxis.

CONCLUSIONS

Bimonthly IV pentamidine for PCP prophylaxis in the HCT pediatric population has comparable safety to monthly IV pentamidine and was highly effective, including in the very young. Bimonthly IV pentamidine should be considered in pediatric patients as second-line PCP prophylaxis.

Dapsone-Induced Methemoglobinemia in a Patient with Acute Lymphocytic Leukemia Admitted with Severe Legionella Pneumonia

Dapsone is an antibacterial medication used as an alternative to the first-line therapy (sulfamethoxazole-trimethoprim) for Pneumocystis pneumonia prophylaxis. Methemoglobinemia is a known toxicity of dapsone. However, dapsone-induced methemoglobinemia in an acute lymphocytic leukemia (ALL) patient with severe Legionella pneumonia has not been previously reported. We describe a 37-year-old male with ALL who was admitted for severe Legionella pneumonia sepsis, rhabdomyolysis, and multiple organ failure. The patient was started on broad-spectrum antibiotics and subsequently intubated for respiratory failure. The patient's methemoglobin level was 24.5%. The repeat methemoglobin level was 28.7%; intravenous methylene blue 100 mg was given for a total of 2 doses after which the methemoglobin level decreased to 2.5%. The patient was extubated 4 days after the second dose of methylene blue. He was later discharged home in stable condition. This patient developed severe sepsis with multiorgan failure, which resulted in acute liver and renal insufficiencies. The decreased metabolism and excretion of dapsone and its toxic metabolite is the likely cause of methemoglobinemia in this patient. Immunocompromised oncology patients who develop severe sepsis require careful monitoring for dapsone-induced methemoglobinemia. Liver dysfunction and renal failure may both potentiate toxicity with prophylactic doses of dapsone.

Dapsone-induced methemoglobinemia: a primer for clinicians

OBJECTIVE

To present a comprehensive review of dapsone-induced methemoglobinemia and its management.

DATA SOURCES

Literature retrieval was accessed through MEDLINE (1966-March 2011), Cochrane Library, and EMBASE, using the terms dapsone and methemoglobinemia.

STUDY SELECTION AND DATA EXTRACTION

All case reports, small case series, and randomized controlled trials published in English were evaluated. Because of the absence of comprehensive updates on this topic since 1996, publications between 1997 and March 2011 were included in this review.

DATA SYNTHESIS

Between 1997 and March 2011, the majority of publications describing methemoglobinemia associated with dapsone use reported this adverse effect at therapeutic doses. Excluding overdose situations, 18 described symptomatic dapsone-associated methemoglobinemia and clinical presentation ranging from cyanosis to dyspnea. In almost all of the accounts, patients had a concurrent event such as anemia or pneumonia, suggesting an interplay between these comorbidities and the onset of symptomatic methemoglobinemia. Delayed hemolytic anemia was seen in patients with high methemoglobin levels at presentation. Management in most cases consisted of administration of methylene blue. Overall, most reports described a successful outcome, and no mortality resulted from methemoglobinemia associated with therapeutic use.

CONCLUSIONS

Clinicians should recognize methemoglobinemia as an adverse effect associated with dapsone use and the potential factors that precipitate it. They should also know how to promptly and effectively manage this event.

Dapsone-induced methemoglobinemia: a dose-related occurrence?

BACKGROUND

Dapsone, used for Pneumocystis jiroveci (PCP) prophylaxis, is associated with increased risk of methemoglobinemia. Absence of cytochrome b5 reductase enzyme activity causes congenital methemoglobinemia, but its role in dapsone-associated methemoglobinemia is unknown. The authors sought to elucidate drug-related risk factors for dapsone-associated methemoglobinemia in pediatric oncology patients, including contribution of cytochrome b5 reductase enzyme activity.

METHODS

Among 167 pediatric patients treated for hematologic malignancies or aplastic anemia who received dapsone for PCP prophylaxis, demographic and dapsone treatment data were retrospectively collected. Drug-related risk factors were evaluated by Cox proportional hazards, and in a cross-sectional subgroup of 40 patients, cytochrome b5 reductase enzyme activity was assessed.

RESULTS

Methemoglobinemia (median methemoglobin level = 9.0% [3.5-22.4]) was documented in 32 (19.8%) patients. There was a 73% risk reduction in methemoglobinemia with dosing ≥20% below the target dose of 2 mg/kg/d (hazard ratio [HR], 0.27; 95% confidence interval [CI], 0.09-0.78; P = .016), whereas methemoglobinemia risk was increased with dosing ≥20% above the target dose (HR, 6.25; 95% CI, 2.45-15.93; P < .001). Sex, body mass index, and age were not associated with increased risk. Cytochrome b5 reductase enzyme activity did not differ by methemoglobinemia status (median 8.6 IU/g hemoglobin [Hb]; [5.5-12.1] vs 9.1 IU/g Hb; [6.7-12.7]). No patient developed PCP on dapsone.

CONCLUSIONS

Methemoglobinemia occurred in almost 20% of pediatric oncology patients receiving dapsone for PCP prophylaxis. Higher dapsone dosing is associated with increased risk. A cross-sectionally acquired cytochrome b5 reductase enzyme activity level was not associated with methemoglobinemia risk. Studies are needed to define biologic correlates of methemoglobinemia and evaluate lower dapsone doses for PCP prophylaxis.

Dapsone induced methemoglobinemia in a patient with glioblastoma

Primary brain tumor patients have multiple risk factors for Pneumocystis jiroveci and may require prophylaxis with TMP-SMZ or dapsone. Although dapsone is generally safe and efficacious, we present a case of a patient diagnosed with a brain stem glioblastoma who developed methemoglobinemia and haemolytic anemia after presenting with worsening confusion and cardiopulmonary system dysfunction. This case highlights one of the potentially severe complications associated with dapsone therapy. Although this illustrates an unusual toxicity of dapsone, a high index of suspicion should be given to high-risk patients due to ethnic heritage, anemia, or advanced age. Furthermore, given the toxicities of TMP-SMZ and dapsone, further work is needed to determine the threshold CD4(+) count at which empiric prophylaxis should be initiated.