The purpose of the study is to characterize the pharmacokinetics of meropenem and piperacillin in ICU-patients at the time of the first dose administration and to contrast that with the same measurements obtained in the same patient 2-3 days later during the course of ICU treatment.

Inclusion Criteria:

- Patient being treated in one of the participating ICUs and planned to recieve treatment with meropenem or piperacillin.

Exclusion Criteria (fullfilling any exlusion criteria means that patient cannot be included in the study):

• Not possible to retrospectively ask the patient or next of kin for consent to take part in the study or patient or next-of-kin not providing consent.
• Not posisble to obtain and process blood samples as specified by protocol.
• Ongoing renal replacement therapy.
• Patient having received the same antibiotic within the previous 96 h.

ICU-patients.