Therapeutic drug monitoring of gentamicin and amikacin in hospitalised patients in a private hospital, Western Cape

Abstract

Background: The burden of resistant bacteria is increasing and to ensure optimal treatment with the antibiotics currently available, therapeutic drug monitoring should be performed when prescribing aminoglycosides. Aminoglycosides are very effective in treating resistant gram-negative bacteria, but their use is limited by toxicity. Therapeutic drug monitoring (TDM) is essential to ensure that aminoglycoside peak concentrations are high enough for effective antimicrobial treatment and trough levels are low enough to minimise toxicity. Toxicity of aminoglycosides include reversible renal toxicity and irreversible ototoxicity. Inappropriate utilisation of TDM may lead to suboptimal therapy, toxicity and waste of resources that are already scarce in South Africa. The study aim was to investigate the standard of aminoglycoside TDM in a South African private hospital. The study determined whether dosage changes were made when the drug levels were outside the normal ranges, whether TDM was being done according to guidelines, and if samples were drawn at the correct times. Method: Retrospective data from November 2014 to October 2016 was used in this observational, descriptive, cross-sectional study, performed in a 221-bed private hospital in the Western Cape. All adult patients, older than 18 years, who were treated with intravenous amikacin or gentamicin for more than 48 hours, were included. A computerised database and patient files were used to obtain the information required for this study. Descriptive statistical analyses were used to describe and summarise data. Results: One hundred and three (103) patients were included: 65 patients on gentamicin and 38 on amikacin. Blood levels were performed on only 19 gentamicin (29.23%) and 22 amikacin (57.89%) patients. Trough levels were taken more than 2 hours before the next dose in 12 gentamicin (63.16%) and 12 amikacin (54.54%) patients. The majority of patients (96.92% on gentamicin and 84.21% on amikacin) received once daily doses. Therapeutic drug monitoring was performed in all patients with an estimated glomerular filtration rate (eGFR) lower than 60 mL/min/1.73m2 and in 23.31% of gentamicin patients and 56.76% of amikacin patients with an eGFR higher than 60 mL/min/1.73m2. All samples taken were trough levels and no peak levels were done. If a blood level was too high, the next dose was omitted. Conclusions: Incorrect sampling times and unnecessary levels taken in patients with normal renal function indicate a need for aminoglycoside treatment guidelines in the private hospital.