Case report:
This is 11 years old boy with a past medical history of hypothyroidism, seizure disorder and hypoxic-ischemic encephalopathy secondary to upper airway obstruction (epiglottitis) with prolonged hypoxemia, tracheostomized on mechanical ventilation at home a few years back.
The patient was admitted due to bradycardia and low potassium level. During hospitalization, the patient developed septic shock and required inotropic support, on day 16 of admission, the patient developed pseudomonas aeruginosa VAP and was treated successfully with piperacillin/tazobactam for 10 days. In between patient developed a picture of sepsis with negative cultures and received different courses of antibiotics.
On hospital day 43 he developed respiratory distress with an increase in oxygen requirement and doses of inotropic support. Upon further evaluation, his inflammatory markers started to elevate with remarkable chest x-ray changes in a form of left retrocardiac airspace disease with bilateral pleural effusion. Thus, the patient was started empirically on piperacillin/tazobactam, gentamicin and vancomycin to cover a possible hospital-acquired infection and VAP. After three days, the respiratory culture showed growth of stenotrophomonas maltophilia and therefore the patient was started on Sulfamethoxazole/ Trimethoprim (SMX/TMP) 5 mg /kg/ every 6 hours. After 3 days of initiation of Sulfamethoxazole/ Trimethoprim, the patient had an episode of desaturation and cyanotic dusky color with no improvement despite ventilator setting adjustment. The patient’s laboratory results were normal except for having metabolic acidosis with a methemoglobin level of 2.7 %.
After discontinuation of SMX/TMP and administration of a methylene blue dose of 1 mg/kg intravenously for the treatment of methemoglobinemia, the methemoglobin level decreased to 0.6 %, and the fraction of inspired oxygen returned back to the normal range. We believe that improvement of oxygenation and methemoglobin levels after discontinuation of SMX/TMP along with administration of methylene blue is due to drug-induced methemoglobinemia by SMX/TMP.