Objective from this study to compare the clinical outcomes and safety between colistin and tigecycline for multi-drug resistant gram negative bacteria.

Study will be in Beni-Suef university hospital. Group I: 66 patients received intravenous colistin 300 mg colistin base activity (CBA) as loading dose, followed by 2.5-5mg/kg/day of CBA in 2 divided doses as a maintenance dose in intensive care unit to treat their MDR infection and group 2 contains 66 patients received intravenous tigecycline100 mg single dose as loading dose, followed by 25-50 mg every 12 hours maintenance dose in intensive care unit to treat their MDR infection

Inclusion criteria:

Study will include

• adult patient (male, female)
• age from 18 to 70 years
• Patients admitted to intensive care unit in study period (six months) who received intravenous colistin or tigecycline as antimicrobial drug for treatment their MDR gram negative infection.

Exclusion criteria:

• Patient admitted to intensive care unit younger than 18 years or older than 70 years.
• Liver transplantation patients.
• Patients are chronic kidney disease (CKD on hemodialysis or baseline creatinine clearance (crcl) < 10 ml/min (estimated by Cockcroft Gault equation).
• Patients received renal replacement therapy before or during admission.
• Patient is on any other nephrotoxic drug (vancomycin, aminoglycosides, NSAIDs, cyclosporine, amphotericin B, etc.).
• Pregnant and lactating women.
• Patients refused the consent of the study.