Comparative Study of Clinical Outcomes and Safety Between Colistin and Tigecycline

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.