Background: Acute-on-chronic liver failure (ACLF) is a severe, rapidly progressing syndrome in patients with liver cirrhosis, often triggered by bacterial infections. Piperacillin/Tazobactam is a key antibiotic in this setting, and therapeutic drug monitoring (TDM) helps optimize its dosing. This study evaluates the impact of an interprofessional TDM strategy for Piperacillin/Tazobactam in ACLF patients in the ICU. Methods: This retrospective ICU study evaluated an interprofessional TDM approach for optimizing Piperacillin/Tazobactam dosing in critically ill ACLF patients. The team, consisting of physicians, clinical pharmacists, and staff nurses, engaged in shared decision making, collaboratively interpreting TDM results and adjusting the dosing accordingly. This study included 26 patients with ACLF who underwent initial TDM and 7 who received follow-up TDM. Piperacillin/Tazobactam dosing was modified based on TDM recommendations, with serum concentrations measured weekly. Adherence to and the implementation of interprofessional dosing recommendations were systematically analyzed to assess the impact of this approach. Results: The initial TDM showed that 30.8% of patients had Piperacillin/Tazobactam levels within the target range, while 53.8% were above and 15.4% below. The interprofessional team recommended dose reductions in seven patients, increases in three, and no change in eleven, with five requiring antibiotic modifications. At the first follow-up TDM, 20.0% reached target levels, while 80.0% remained above, with no subtherapeutic cases. The team recommended one further dose reduction and maintained dosing in four patients. All recommendations were fully implemented, demonstrating strong adherence to the collaborative protocol. Conclusions: The interprofessional TDM strategy optimized Piperacillin/Tazobactam dosing in ACLF patients with full adherence to the recommendations. This collaborative approach improves outcomes and supports global efforts to curb antibiotic resistance.