Nalidixic acid overdose and metabolic acidosis

Letters

CJEM 2006;8(2):78

To the editor: A 15-year-old boy was recently brought to our emergency centre with lethargy and agitation after ingesting about 60 tablets of nalidixic acid (NA) in a suicide attempt. Shortly after arriving, he suffered a tonic-clonic seizure requiring intravenous diazepam. In addition to altered mentation, he was tachypneic with a respiratory rate of 40 beats/min. Cardio- vascular, gastrointestinal and neurologic examinations were normal, and blood glucose was 100 mg/dL. Arterial blood gas analysis revealed a pH of 7.31, PCO 2 of 11.3, [HCO 3 ] of 5.7, PO 2 of 98.7 and oxygen saturation of 96%. Because of the profound metabolic acidosis, he was treated with 44 mEq of sodium bicarbonate (NaHCO 3 ). With supportive care, the boy recovered uneventfully after 12 hours.

Nalidixic acid poisoning may cause altered mentation, psychosis, convulsions and, rarely, metabolic acidosis.^1-4 Quinolones inhibit GABA (gamma-aminobutyric acid) receptors in the human central nervous system, potentially precipitating seizures.² Nalidixic acid interferes with lactate metabolism and may cause acidosis in predisposed patients,^3,4 although, in this case, the acidosis may have been in part due to seizure and agitation. Sodium bicarbonate was administered intravenously because of concerns about acidosis-related myocardial and central nervous system dysfunction,⁵ but it is unclear whether this therapy was beneficial. Nalidixic acid poisoning is an uncommon problem, but should be considered in the differential diagnosis of patients presenting with unexplained metabolic acidosis and seizures. NA should not be prescribed in patients who have a propensity to develop acidosis, particularly patients with poor perfusion, sepsis or liver disease.

Nastaran Eizadi-Mood
Poisoning Emergency Center
Noor and Ali Asghar Hospital
Isfahan, Iran; izadi@med.mui.ac.ir

Farzad Gheshlaghi
Isfahan University of Medical Sciences
Isfahan, Iran