Sepsis is one of the most common cause of mortality in PICUs  worldwide. Although many children are admitted in critical care units with sepsis or related complications, nosocomial sepsis contributes a significant burden with incidence of 2.8-21.6% as per various studies. Bacterial sepsis constitutes the majority of nosocomial infections. Ventilator associated pneumonia (VAP) is among the most frequently occurring nosocomial infection in the PICU and has been associated with increased morbidity, prolonged duration of ventilation and increased cost. Although both gram positive and negative organisms are known to cause VAP, gram negative pathogens predominate in the PICU settings.. Resistant Gram negative pathogens  in PICU have emerged as a significant problem over the past few decades. Colistin has reemerged as a useful antibiotic for resistant gram negative organisms and now represents a therapy of last resort. The standard practice is to administer intravenous colistin in intermittent dosing thrice a day. The use of continous infusion method has been documented in some clinical studies. The  clinical VAP diagnosis as well as outcome is currently assessed by Clinical Pulmonary Infection Score described first by Pugin et al¹³. Presently in our hospital we deal with a large number of patients with VAP caused by gram negative organisms. The recent emergence of drug resistant strains has been a concern leading to use of colistin as per our present PICU antibiotic protocol. The concept of loading dose and time averaged long exposures have been suggested in past studies as the basis of continous infusion colistin protocol. This study will be a time bound study conducted over a period of one year in  a 12-bed multidisciplinary pediatric critical care unit (PICU) at Sir Ganga Ram hospital in Delhi after obtaining ethical clearance. Children of age 1 month to 18yrs suffering from VAP as per CPIS score and microbiological evidence will be included. They will be randomized into receiving intermittent and continous dosing of colistin. Endpoints will be negative CPIS scores and microbiological clearance at completion of therapy.