Vancomycin is currently the drug of choice in meticillin-resistant Staphylococcus aureus (MRSA) infection. It is also used prophylactically in some situations in which the patient is at risk for endocarditis. It is often used in combination with other antibacterials in the treatment of endocarditis and is a potential nephrotoxin. Various consensus guidelines differ in their interpretation of vancomycin plasma concentrations. This paper describes a case of a 72-years old Caucasian female patient, who developed significant renal impairment when prescribed vancomycin in combination with penicillin for the treatment of endocarditis, caused by Streptococcus pneumoniae.