Dosing of piperacillin/tazobactam in a morbidly obese patient

The combination of piperacillin and tazobactam has been shown to be efficacious for the treatment of intra-abdominal infections, skin and soft tissue infections, bacteraemia and pneumonia. The pharmacokinetics (PK) of piperacillin/tazobactam have been extensively investigated in both healthy volunteers and in distinct patient settings. 1 Like other b-lactams, piperacillin/tazobactam displays time-dependent pharmacodynamics (PD), whereby duration of time that concentrations remain above the MIC correlates best with bacterial kill and efficacy. The PK/PD target associated with a high probability of therapeutic success is defined as free concentrations above the MIC for 50% of the dosing interval (50% fT .MIC). 2 In case of more severe infections or when poor penetration into infected tissues is expected, 30%‐ 40% fT . 4‐5 ×MIC should ideally be attained. 2 It is not clear whether these targets are reached in morbidly obese patients as published information on optimal dosing in this subset of patients is rare. A 33-year-old morbidly obese patient (220 kg, 1.9 m and body mass index 55 kg/m 2 ) was transferred to our orthopaedic ward with a surgical site infection following a transfemoral amputation of the left leg following a car accident. He has provided written, informed consent for the details given here to be published. The patient had been empirically started on amoxicillin/ clavulanic acid; however, despite 8 days of treatment, necrosis increased and markers of infection were still raised (C-reactive