How should antibiotics be dosed in obesity?

The Q&A produced in 2013 has been updated and published on the Scottish Antimicrobial Prescribing Group (SAPG) website. A review of the evidence was carried out in 2016 using the same literature search strategy by the Association of Scottish Antimicrobial Pharmacists and Healthcare Improvement Scotland. This Q&A summarises the available evidence for several classes of antibiotics.

  • Obesity results in physiological changes that can affect the volume of distribution and the clearance of many antibiotics. The extent of these changes is variable and depends upon patient characteristics (e.g. degree of obesity, underlying organ function) and the chemical properties of the antibiotic. Antibiotic concentrations achieved with conventional dosages may therefore differ significantly between obese and non-obese patients.
  • Manufacturers do not routinely provide guidance on the dosing of drugs in obesity.
  • Data and guidance regarding the pharmacokinetics, pharmacodynamics and dosing recommendations of most antibiotics in obesity is limited, making specific dose recommendations for obese patients difficult.
  • There is relatively more guidance available for the dosing of aminoglycosides and vancomycin. This Q&A summarises the available evidence for the following antibiotics: aminoglycosides (amikacin, gentamicin and tobramycin), beta-lactams (penicillins, cephalosporins and carbapenems), quinolones (ciprofloxacin, levofloxacin and moxifloxacin), colistimethate sodium, clindamycin, daptomycin, linezolid, teicoplainin and vancomycin.
  •  Limited data suggest larger doses of certain antibiotics including cephalosporins may be required for surgical prophylaxis in obese patients.
  • The available data needs to be interpreted with caution. For example, it is not known whether results from healthy obese volunteers can be applied to unwell obese inpatients and how the degree of obesity affects the interpretation of results.
  • The type and location of infection may affect the dose regimen required in obese patients.
  •  Therapeutic drug monitoring should be used to guide the dosing of antibiotics in obesity where possible together with the monitoring of clinical response and toxicity. Further studies are needed to provide guidance on how to dose antibiotics in obesity to achieve optimal effectiveness and safety