An Observational Pharmacokinetic Sudy of Ceftolozane-Tazobactam in Intensive Care Unit in Patients With and Without CRRT

The purpose of this study is to try to find out how critically ill patients receiving the antibiotic, ceftolozane-tazobactam, process it in their body. Investigators would like to study if the antibiotic concentrations during a dose of this antibiotic reaches the right concentrations necessary to kill the bacteria that is causing the infection. The process by which a drug travels through the body in blood, how it is broken down and removed by the body is called pharmacokinetics (PK). We can measure the PK by taking blood samples at specific times after the antibiotic is given. Investigators would like to do the study in patients receiving dialysis and patients who are not receiving dialysis. This information about how the antibiotic is processed in the critically ill patient is unknown and it is important to know whether the doses doctors give patients to fight infection are adequate. If antibiotic concentrations are low in the blood, it gives the bacteria an opportunity to become resistant to the antibiotic which can lead to the antibiotic being less effective against bacteria potentially exposing future patients with infections to a limited range of effective antibiotics. Patients will be consented, and given the antibiotic as prescribed. Blood samples will be taken from the drip that is already in the patients arm just as the antibiotic starts, at 15 and 45 minutes, at 1,2,3,4,5,6,7 and 8 hours. Patients who are on dialysis will have the blood samples taken from the dialysis machine before the blood reaches the dialysis filter (same blood samples as the non dialysis patients) and also bloods samples taken after the filter at 45 minutes, 2 and 6 hours. Dialysis patients will also have 5 separate samples of ultrafiltrate taken (approximately 10mls) - ultrafiltrate is the waste product of the dialysis process. The total amount of blood will be 40mls which is equal to about 2 tablespoons. The dialysis patient will have 50mls of blood taken.Information about the patients ICU stay will also be recorded.