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1307 - Amantadine-Bactrim drug interaction presents as possible baclofen pump failure in male patient with a history of anoxic brain injury and recent baclofen pump exchange.

Thursday, February 27, 2025

5:00 PM - 6:30 PM MST

Presenting Author(s)

NM

Naomi McLeod, DO

Resident Physician
UT Health San Antonio
san antonio, Texas, United States

Co-Author(s)

BS

Benjamin Seidel, DO

Program Director, Staff Physician, Polytrauma Rehabilitation Center
PM&R Residency Program, UT Health San Antonio. Audie Murphy VA Polytrauma
San Antonio, Texas, United States

Case Diagnosis: Amantadine toxicity secondary to amantadine-bactrim drug interaction.

Case Description: Here we discuss the case of a patient with prior anoxic brain injury and spasticity who presented to the emergency department three weeks post baclofen pump exchange with a progressive history of worsening lower extremity spasticity, dysarthria, confusion, behavior change, hallucinations, and reduced mobility. Due to concerns of baclofen toxicity or withdrawal secondary to complications associated with the exchange, the patient was admitted for closer monitoring. The patient’s baclofen pump was interrogated and evaluated by neurosurgery and physiatry and deemed unlikely to be the primary cause of this patient’s presenting symptoms. Further history revealed that the patient started Bactrim two days before presentation due to a surgical site infection. It was discovered that Bactrim can increase serum levels of amantadine, increasing the risk of amantadine toxicity.

Discussions: Amantadine is a commonly used neurostimulant in brain injury medicine in the context of traumatic brain injury (TBI), although it has many drug interactions. These drug interactions can lead to changes in serum levels, resulting in toxicity. Baclofen withdrawal and amantadine toxicity can both present with altered mental status, agitation, and abnormal muscle tone, and are associated with an increased risk of cardiac arrhythmia and seizures. This patient had additional symptoms of hallucinations, dysarthria, and myoclonic jerks in the absence of fever or hemodynamic instability, most consistent with amantadine toxicity.

Conclusions: Amantadine and Bactrim were discontinued, and the patient’s presenting symptoms resolved at their discharge follow-up appointment. This case is a reminder of the importance of obtaining a comprehensive history and medication reconciliation, especially in a patient population at risk for polypharmacy.