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Background and Importance Pharmacokinetic monitoring of β-lactam antibiotics is becoming increasingly more relevant, particularly in critically ill patients whose condition entails major physiological alterations.Variability in volume of distribution, renal impairment, and rising resistance rates leading to higher minimum inhibitory concentrations (MIC), making it essential to evaluate whether PK/PD targets are being achieved.Aim and Objectives The objective of this retrospective study is to highlight the relevance of therapeutic drug monitoring (TDM) of β-lactam antibiotics in achieving PK/PD targets, improving treatment efficacy and microbiological eradication, and reducing the risk of adverse effects.Material and Methods A total of 45 adult patients admitted to an intensive care unit and treated with a β-lactam antibiotic were included between February and September 2025 (9 months).Pharmacokinetic monitoring was performed in patients with septic shock, altered renal function, immunosuppression, complicated infections, or infections caused by microorganisms with elevated MICs.Trough levels were obtained in patients on extended infusion, as well as steady-state concentrations in those receiving continuous infusion. After the first 24 hours, doses were adjusted according to renal function in patients with reduced renal clearance or undergoing continuous renal replacement therapy (CRRT).Data collected included age, sex, type of infection, antibiotic used, type of infusion, plasma concentration, and pharmacist intervention.Results 45 patients were included, of which 66% (n=30) were male. Mean age was 70 (). 49% (n=22) of patients received empirical treatment, whilst 51% (n=23) received targeted therapy. 15 patients received cefepime, of which 53% (n=8) required dose adjustment, and 6% (n=1) required a type of infusion change to continuous infusion.Two patients received ceftazidime, of which 50% (n=1) required dose reduction. 27 patients received meropenem, of which 18% (n=5) required dose reduction and 7% (n=2) required dose increase. One patient on ampicillin required dose reduction.Out of all patients, an overall of 40% (n=18) required dose adjustment.Conclusion and Relevance Therapeutic drug monitoring (TDM) of β-lactam antibiotics is essential to optimise antibiotic therapy in critically ill patients with complicated infections. Despite the use of maximum recommended doses, some patients required even higher doses to achieve therapeutic targets.A considerable proportion of patients required dosage adjustments based on pharmacokinetic results.Conflict of Interest No conflict of interest