What is the most likely cause of myoclonus and disorientation in a patient with chronic kidney disease (CKD) and impaired renal function, who was treated with cefepime (a fourth-generation cephalosporin antibiotic) for a urinary tract infection (UTI)?

Medication-Induced Neurotoxicity (Cefepime)

The most likely cause of this patient's myoclonus and disorientation is cefepime-induced neurotoxicity (Answer B), and the drug should be discontinued immediately.

Clinical Reasoning

This patient presents with the classic triad of cefepime neurotoxicity:

• Myoclonus - a hallmark neurological manifestation 1
• Altered mental status with disorientation to place and time 2, 1
• Stage 3b CKD (baseline creatinine 1.86 mg/dL) - the primary risk factor for drug accumulation 3, 4

The temporal relationship is characteristic: symptoms developed on hospital day 5, which falls within the typical 1-10 day window for cefepime neurotoxicity 1, 5. Critically, neurotoxicity occurs even when cefepime is appropriately dose-adjusted for renal function in 26% of cases 4, and this patient received "renally dosed" cefepime yet still developed toxicity.

Why Other Diagnoses Are Less Likely

Sepsis-associated encephalopathy (C) is excluded because:

• The infection clinically resolved within 24 hours [@case presentation@]
• Leukocytosis normalized by day 5 [@case presentation@]
• Vital signs are now normal [@case presentation@]
• The patient is afebrile [@case presentation@]

Uremic encephalopathy (D) is excluded because:

• Renal function remained stable at baseline (creatinine 1.86 mg/dL unchanged) [@case presentation@]
• Stage 3b CKD alone does not typically cause acute encephalopathy without further deterioration [@case presentation@]

Nonconvulsive status epilepticus (A) can be a manifestation of cefepime toxicity itself 2, 5, but is not the primary diagnosis - it would be secondary to the drug toxicity.

Immediate Management

Discontinue cefepime immediately 2. The FDA drug label explicitly states: "If neurotoxicity associated with cefepime therapy occurs, discontinue cefepime and institute appropriate supportive measures" 2.

Expected clinical course:

• Neurological symptoms typically resolve completely after cefepime discontinuation 3
• Recovery usually occurs within 48 hours 6
• In severe cases with very high drug levels, consider hemodialysis to accelerate drug removal 6

Critical Risk Factors Present in This Patient

• Chronic kidney disease - present in 66.7% of neurotoxicity cases versus 35.3% without neurotoxicity (P = 0.04) 1
• Elderly age - 72 years old is a recognized risk factor 5
• Inadequate dose adjustment - occurs more frequently when dosing is not properly adjusted (P = 0.001), though can still occur despite appropriate adjustment 1

Alternative Antibiotic Selection

For future Pseudomonas coverage in this patient with recurrent UTIs and CKD:

• Piperacillin-tazobactam has lower seizure risk (11% relative pro-convulsive activity versus cefepime's 160%) 3
• Meropenem has lower neurotoxicity risk (16% relative pro-convulsive activity) 3
• Avoid cefepime in patients with CKD and history of seizures or neurological disorders 3

Key Clinical Pitfall

The most dangerous pitfall is attributing altered mental status to other causes (sepsis, uremia, delirium) in critically ill patients receiving cefepime, leading to continued drug exposure and worsening neurotoxicity 5. Myoclonus is the key distinguishing feature - when present with altered mental status in a patient on cefepime, neurotoxicity should be the presumed diagnosis until proven otherwise 1.