This case report details the case of a 70-year-old man with Marfan syndrome and hypertension who developed neutropenia after an eight-week course of ceftriaxone, used to treat a brain abscess. Initially presenting with tonic-clonic seizures and headaches, his condition was managed with ceftriaxone and metronidazole. The subsequent drop in neutrophil counts from 7.54 × 10^9/L to 0.87 × 10^9/L leads to the discontinuation of ceftriaxone and the administration of granulocyte-colony stimulating factor (G-CSF), which effectively restored the neutrophil levels. This case highlights that clinicians should be aware of ceftriaxone-induced neutropenia as a potential complication, especially in patients undergoing prolonged therapy. Regular monitoring and timely management are essential for patient safety and favorable outcomes.