1) To compare the efficacy of ertapenem with respect to the overall microbiological response assessment profile in the treatment of patients with serious (requiring hospitalization and treatment with parenteral therapy) complicated UTIs, including acute pyelonephritis, with that of the meropenem control group at the 5 to 9 days posttherapy (EFU/TOC) follow-up visit. 2) To compare the efficacy of ertapenem with respect to the clinical response assessment profile in the treatment of patients with serious complicated UTIs, including acute pyelonephritis, with that of the meropenem control group at completion of parenteral therapy (DCIV). 3) To compare the efficacy of ertapenem with respect to the overall microbiological response assessment profile in the treatment of patients with serious complicated UTIs, including acute pyelonephritis, with that of the meropenem control group at DCIV. 4) To evaluate the safety profile of ertapenem at DCIV.