 Urine will be collected and split into two aliquots of equal volume and transferred to polypropylene tubes Tube 1 and Tube 2. The tubes will pre-labeled as Tube A Tube 1 and Tube B Tube 2. Tubes will be pre-labeled with indelible ink and include the following information: sample type urine, protocol number, and subject number. Samples will be stored frozen at -20 degrees Centigrade until they are shipped for ertapenem concentration determination. 