Traditional β-lactam antibiotic dosing does not consider physiological changes in medical conditions such as sepsis. Optimal antibiotic exposure could be achieved by therapeutic drug monitoring (TDM). This review gives a brief summary. Current studies are sparse, but suggestive of a potential beneficial role of TDM to patients with reduced renal function, obese patients and the critically ill. TDM can potentially reduce adverse effects and optimise antibiotic exposure. However, standardised TDM methods are lacking and randomised clinical studies are warranted in order to prove clinical benefit.