Protracted methemoglobinemia after phenazopyridine overdose in an infant

Acquired methemoglobinemia: A systematic review of reported cases

INTRODUCTION

Acquired methemoglobinemia may cause cyanosis and tissue ischemia unresponsive to oxygen supplementation.

METHODS

We performed a literature search to identify cases of acquired methemoglobinemia published between 1980 and 2020. Clinical, diagnostic, and treatment details were extracted from eligible cases.

RESULTS

A total of 76 reports involving 87 cases were analyzed. The median age at presentation was 32.5 with male to female ratio of 1.6. Cyanosis and SpO₂ <90 % were reported in 82 % and 60 % of cases, respectively. Dapsone or cocaine-based anesthetics were causative in 52 % of cases; most anesthetic-related cases occurred in the peri-procedural setting. Methylene blue (MB) and red cell transfusion were given in 71 % and 10 % of cases, respectively. Compared to MB untreated patients, MB treated patients were more likely to be cyanotic (91.9 % vs 54.2 %), had higher proportions (%) and levels (g/dL) of methemoglobin (MetHb) - 33.2 % vs 15.3 % and 3.1 g/dL vs 1.2 g/dL, respectively. We found that among cyanotic cases, the median MetHb level was 3.0 g/dL (0.4-12.3 g/dL) with 74 % of values ≥ 1.5 g/dL. An SaO2:SpO₂ ratio of >1 was not universally present, but always coincided with an [SaO₂-SpO₂] delta value greater than zero.

CONCLUSIONS

Cyanosis and hypoxemia were not universal findings of acquired methemoglobinemia in our series. In addition, not all patients had cyanosis at MetHb ≥ 1.5 g/dL or an SaO2:SpO₂ ratio of >1. All those with an SaO₂:SpO₂ >1 did, however, have a delta value greater than zero - a finding not previously reported which we feel holds diagnostic value.

Acquired methemoglobinemia: a retrospective series of 138 cases at 2 teaching hospitals

Methemoglobin is a form of hemoglobin that does not bind oxygen. When its concentration is elevated in red blood cells, functional anemia and tissue hypoxia may occur. We performed a retrospective case series to describe the cases of acquired methemoglobinemia (methemoglobin level >2%) detected and the clinical circumstances under which they occurred at 2 tertiary care hospitals and affiliated outpatient clinics over 28 months. We surveyed co-oximetry laboratory data to identify patients with methemoglobinemia. We reviewed these patients' medical records to extract the clinical information and context. One hundred thirty-eight cases of acquired methemoglobinemia were detected over the 28 months. There was no gender predisposition, and the condition occurred over a wide range of ages (patients aged 4 days to 86 years). Cases occurred in many areas of the hospital, including outpatient clinics. One fatality and 3 near-fatalities were directly attributable to methemoglobinemia. Dapsone was the most common etiology of acquired methemoglobinemia, accounting for 42% of all cases. The mean peak methemoglobin level among these individuals was 7.6%. In 5 of the patients with the most severely elevated levels, 20% benzocaine spray (Hurricaine Topical Anesthetic spray, Beutlich Pharmaceuticals, Waukegan, IL) was the etiology, associated with a mean peak methemoglobin level of 43.8%. Eleven pediatric patients developed methemoglobinemia either from exogenous exposure, such as drugs, or due to serious illness, such as gastrointestinal infections with dehydration. Almost all (94%) patients with methemoglobinemia were anemic. Drugs that cause acquired methemoglobinemia are ubiquitous in both the hospital and the outpatient setting. Acquired methemoglobinemia is a treatable condition that causes significant morbidity and even mortality. We hope that a heightened awareness of methemoglobinemia will result in improved recognition and treatment. Primary prevention efforts have the potential to reduce the morbidity and mortality associated with this condition.

Methemoglobinemia due to ingestion of at most three pills of pyridium in a 2-year-old: case report and review

Pyridium (phenazopyridine HCl) is a commonly prescribed medication in the treatment of urinary tract infections and is known to cause methemoglobinemia in excessive doses. We report the case of a 2-year-old child who ingested a maximum of three 200-mg tablets (approximately 50 mg/kg) of pyridium and yet developed cyanosis and methemoglobinemia (29.1%), resulting in methylene blue therapy. We urge physicians to consider a period of observation (4-6 h) or to obtain methemoglobin levels in children who ingest even a small number of pyridium tablets because this can represent a toxic dose in a small child.