Linezolid-associated severe hyperlactatemia masked by metabolic alkalosis in a geriatric patient: a case report.

BACKGROUND

Linezolid-induced hyperlactatemia may be masked by metabolic alkalosis, creating diagnostic challenges. This case demonstrates how acid-base disturbances can delay toxicity recognition in geriatric patients.

CASE PRESENTATION: An 82-year-old Han Chinese woman with carbapenem-resistant Acinetobacter baumannii pneumonia developed severe hyperlactatemia (peak 17 mmol/L) during linezolid therapy (600 mg every 12 hours for 14 days). Despite progressive lactate elevation (1.6 → 17 mmol/L), alkalotic pH (7.45-7.51) and normal anion gap (8-12 mmol/L) obscured the diagnosis.

INTERVENTIONS: Serial monitoring included arterial blood gas analysis and serum lactate levels. Linezolid was discontinued upon recognition of hyperlactatemia. Continuous renal replacement therapy was initiated post-discontinuation.

OUTCOMES: A lactate/HCO3- ratio > 0.17 (day 20) preceded metabolic decompensation by 5 days. Renal replacement failed to correct lactate accumulation, suggesting irreversible mitochondrial damage.

CONCLUSION

pH-based monitoring inadequately detects linezolid toxicity in alkalotic patients. Lactate/HCO3- ratios (> 0.17) should be incorporated into geriatric antimicrobial protocols for early intervention.