The purpose of this study is to determine whether inhaled colistin is effective in the treatment of ventilator associated tracheobronchitis due to gram negative organism susceptible to colistin.

Patients diagnosed ventilator-associated tracheobronchitis due to gram negative organism are included to the study.The patients will be received colistin inhalation 75 mg every 12 hours at least 5 days.

The primary objective is to evaluate clinical outcome of inhaled colistin. The secondary objectives are microbiological clearance and toxicity of inhaled colistin.

The sample size was estimated to 62 patients.

Inclusion Criteria:

• Clinical diagnosis of ventilator-associated tracheobronchitis caused by gram negative organism.
• Expected to survive more than 48 hours after enrollment.
• Received intravenous colistin not more than 48 hours prior enrollment.

Exclusion Criteria:

• Pregnancy and Lactation
• Allergy to colistin
• Serum creatinine > 4 mg/dl or GFR decreased more than 75% from baseline