This prospective, comparative study is evaluating the effectiveness and adverse effects of using colistin at a loading dose of 9 million international units (MIU) followed by 4.5 MIU every 12 h (q12 h) + tigecycline at a loading dose of 100 mg followed by 50 mg every 12 h (q12 h) versus colistin + meropenem 2 g q8 h in treating blood stream infections due to multidrug-resistant (MDR) Klebsiella pneumoniae. The aims of the current study are to investigate and evaluate the therapeutic activity and side effects of Colistin-Meropenem combined therapy versus Colistin-Tigecycline combined therapy in treatment of patients with Multiple Drug Resistant (MDR)-Klebsiella pneumonia bacteraemia The primary goal is comparing 14 day mortality between critically ill patients with MDR Gram-negative Klebsiella pneumoniae infection as evaluation of the therapeutic activity of colistin - tigecycline vs. colistin - meropenem combined therapies. The secondary goal is comparing the comorbidities (nephrotoxicity, hepatotoxicity, neurotoxicity, hematological changes) between critically ill patients with MDR Gram-negative Klebsiella pneumoniae infection who will be treated with colistin - tigecycline versus colistin - meropenem combined therapies.

Method: A total of 60 patients were divided into two groups (30 patients each); the first group received Intravenous colistin 9 MIU IV infusion over 2 hours loading dose followed by maintenance dose 4.5 MIU IV infusion over 2 hours q12 h plus Intravenous Tigecycline 100 mg IV infusion over 1 hour loading dose followed by maintenance dose 50 mg IV infusion over 1 hour q12 and the second group received Intravenous colistin 9 MIU IV infusion over 2 hours loading dose followed by maintenance dose 4.5 MIU IV infusion over 2 hours q12 h plus Intravenous meropenem 2 g IV infusion over 30 minutes q8 h

Inclusion Criteria:

• Patients with blood stream infection caused by MDR K. pneumoniae, as defined by Infectious Diseases Society of America (IDSA), who were hospitalised in the general ICU, confirmed with carbapenem-resistant K. pneumoniae-positive culture results from blood sample within the previous 5 days

Exclusion Criteria:

• All patients without a MDR carbapenem-resistant K. pneumoniae-positive culture isolated from the blood. In addition, the following patients are excluded: patients with a Glasgow Coma Scale (GCS) score of <9 in non-ventilated patients or <6 in ventilated patients; patients with end-stage metastatic malignant cancer; and all terminal patients with Acute Physiology and Chronic Health Evaluation (APACHE) II or Sequential Organ Failure Assessment (SOFA) scores of >34 or >15, respectively, and risk of mortality >85% or >80% on the first day of colistin administration, respectively [27,28]. Moreover, patients who received i.v. colistin combination therapies for <72 h are excluded from further analysis

single-blind