Objective: To report the pharmacokinetics of gentamicin using traditional multiple daily doses and a high-dose regimen in an elderly patient. Clinical Presentation and Intervention:An 80-year-old male who presented with mild renal failure received two different gentamicin dosing regimens, 60 mg every 8 h for septicemia and a high dose of 400 mg with extended interval for suspected endocarditis. Based on population parameters of k_e (0.1030 h^–1) and V_d (18.1 liters), the initial gentamicin dosage regimen was calculated to be 80 mg every 12 h. The measured peak and trough concentrations were used to calculate the individual parameters of k_e (0.0749 h^–1) and V_d (30.9 liters). After a 5-mg·kg^–1 gentamicin dose, the Hartford nomogram was used to estimate the extended dosage interval. Conclusion: The Hartford nomogram may be a valid tool for estimating the dosage interval after a 5-mg·kg^–1 single dose of gentamicin.