Inclusion Criteria:  Adult (≥18 years old) ICU patients Confirmed or suspected either community-acquired pneumonia, ventilator-associated pneumonia, aspiration pneumonia or a clinically diagnosed lung infection Patient has been prescribed or is receiving one of the study drugs (benzylpenicillin, ceftriaxone, meropenem, or piperacillin/tazobactam) for the treatment of pneumonia in the ICU Patient is sedated and receiving mechanical ventilation Patient has arterial line and urinary catheter in situ for blood and urine samplings Informed consent to participate in the study  Exclusion Criteria:  Suspected or known hypersensitivity towards beta-lactam antibiotics (pre- or post-enrolment) Receiving renal replacement therapy (RRT) Pregnant patients or lactating mothers Has received study antibiotic for more than 72 hours (at time of Occasion 1) during current infective episode.