This is a multicenter, open-label (identity of treatment is known to patient's parent/legal guardian/caregiver and to all study staff) pharmacokinetic study (a study to observe how the drug is absorbed and distributed within the body) to measure drug levels of doripenem in hospitalized but medically stable infants (term and preterm), <12 weeks of chronological age (CA) (age since time of birth) who have documented, presumed to have, or are at risk for bacterial infection(s) and are undergoing treatment with intravenous (i.v.) (administered in a vein) antibiotics. Doripenem will be administered alone at any time after the first dose of a nonstudy antibiotic is administered to the patient. Doripenem is not being used in this study to treat infection and it will not replace the patient's prescribed antibiotic(s). The duration of the study will be up to 9 days for each patient. Patients' safety will be monitored throughout the study by a safety committee who will review safety information at least once a month or after every 8 patients are enrolled and dosed. Safety evaluation will include, but will not be limited to, adverse events, clinical laboratory tests, and vital signs. A single dose of study drug (doripenem) will be administered to patients in a hospitalized setting. Patients <8 weeks CA will receive a 5 mg/kg doripenem 1-hour i.v. infusion, and patients >=8 weeks CA will receive an 8 mg/kg doripenem 1-hour infusion. Study drug will be administerd to the patient alone at any time after the first dose of a nonstudy antibiotic is administered to the patient.