Catching the Culprit: Benzylpenicillin Neurotoxicity Confirmed by Therapeutic Drug Monitoring in a Critically Ill Patient with Continuous Venovenous Hemofiltration

We present the case of a 65-year-old patient who was treated with high-dose benzylpenicillin for severe invasive pneumococcal pneumonia, complicated by acute renal failure managed with continuous venovenous hemofiltration. After cessation of continuous venovenous hemofiltration, the patient experienced multiple tonic–clonic seizures. Therapeutic drug monitoring revealed high total serum concentrations of benzylpenicillin, identifying it as the likely cause of the neurotoxicity. This case study presents the first documented total serum benzylpenicillin concentration associated with neurotoxicity.