Psychosomatic or Psychotropic Polypharmacy? A Case Highlighting the Importance of Pharmacokinetics

Abstract

<h3>Introduction</h3> Psychotropic drugs are among the most common medications prescribed to elderly patients. The number of psychotropic drugs has increased significantly over the past few decades with a proportional increase in adverse medication outcomes including drug-drug interactions. Advancing age is accompanied by changes in pharmacokinetics and pharmacodynamics that put older patients at greater risk for adverse medication outcomes. The majority of psychotropic agents are metabolized by hepatic enzymes with many drug-drug interactions of psychotropics involving the cytochrome P450 enzyme system. The activity of these enzymes can be inhibited or induced by several drugs resulting in clinically significant drug-drug interactions. This case highlights the importance of maintaining a comprehensive understanding of pharmacokinetics and considering the possibility of an adverse drug reaction when evaluating an older patient presenting with new and unexplained symptoms. <h3>Methods</h3> This case report focuses on a geriatric patient with depression and multiple medical comorbidities presenting with unexplained neurological symptoms thought to be psychosomatic in origin. Patient's clinical documents in our electronic medical records system were reviewed. A literature survey was performed on the topic of psychotropic polypharmacy, pharmacokinetics, and the increased risk of adverse medical outcomes in geriatric patients. <h3>Results</h3> A 69 year old female was referred by inpatient neurology to an outpatient geriatric psychiatry clinic for evaluation and management of psychogenic non-epileptic seizures/conversion disorder. She had been experiencing ongoing symptoms of dizziness, dysarthria, and gait instability with multiple serious falls requiring hospitalization. She underwent an extensive and uneventful medical and neurological workup. Immediately prior to onset of symptoms, the patient was taking the maximum dose of amitriptyline at 150mg when bupropion was added and increased to 300mg. Symptoms were suspected to be secondary to amitriptyline toxicity with bupropion (a potent CYP2D6 inhibitor) leading to supratherapeutic amitriptyline levels (a CYP2D6 substrate). Amitriptyline level was obtained and returned supratherapeutic at 362. Both amitriptyline and bupropion were discontinued with immediate resolution of the patient's neurological symptoms. <h3>Conclusions</h3> Polypharmacy is a disease simulator; patients may exhibit conditions caused by medications rather than organic illness. It is crucial for clinicians to be aware of drug interactions and consider whether the development of a new medical condition could be the presentation of an adverse drug event. Many drug interactions are the result of altered CYP450 metabolism, and therapeutic drug doses may cause adverse effects related to increased drug serum levels if a CYP450 enzyme inhibitor is added or if the patient is a genetically poor metabolizer. Knowledge of the most important drugs metabolized by cytochrome P450 enzymes, as well as the most potent inducers and inhibitors, can help to reduce the occurrence of adverse drug events and interactions.