Asian Journal of Cardiology Research

Aim: This case study aims to highlight the critical role of therapeutic drug monitoring (TDM) and the risks of polypharmacy in older patients, with specific emphasis on the challenges of managing digitalis toxicity in a patient with multiple comorbidities receiving a narrow therapeutic index drug.

Case Presentation: A 70-year-old female with a 15-year history of chronic heart failure and a history of myocardial infarction presented with central chest pain, nausea and persistent vomiting for 2-3 days. Despite normal renal function (creatinine 1.0 mg/dL) and hepatic markers, she had severe bradycardia. Laboratory investigations revealed a toxic serum digoxin level of 2.13 ng/mL. Electrocardiographic (ECG) analysis showed a downward slope of the ST segment beginning from the isoelectric baseline, with an inverse tick sign in leads with positive as well as negative QRS complexes.

Discussion: Digoxin is a narrow therapeutic index drug with a limited therapeutic window (0.5-2.0 ng/mL). In this patient, toxicity was likely exacerbated by advanced age, female sex and a synergistic drug interaction with bisoprolol, as both agents depress atrioventricular (AV) nodal conduction. Although digoxin-specific antibody (Fab) fragments are the definitive treatment, their high cost necessitated successful conservative management through drug withdrawal and chronotropic support with orciprenaline.

Conclusion: In older patients, the potential benefits of digoxin in reducing hospitalisations must be weighed against its significant risk profile. Regular TDM and a high level of clinical suspicion for non-cardiac symptoms, such as nausea, are vital for the early detection of life-threatening bradyarrhythmia.