Ventilator associated pneumonia occurs commonly and nebulized antibiotics are being used for its treatment. Although adequate pulmonary biodistribution is important for antibiotic effect, there is a lack of data for both intravenous (i.v.) or nebulized antibiotic administration during mechanical ventilation.
To describe the comparative pulmonary regional distribution of i.v. and nebulized technetium-99m labelled tobramycin (Tc-tobramycin) 400 mg in a mechanically ventilated ovine model.
The study was performed in a mechanically ventilated ovine model. Tc-tobramycin 400 mg was obtained using a radiolabelling process. Computed tomography (CT) was performed. Five sheep each were given Tc-tobramycin 400 mg via i.v. or nebulized route. Planar images- dorsal, ventral and both lateral- were obtained using a gamma camera. Blood samples were obtained every 15 minutes for one hour (4 time points) and, lung, liver, both kidney, and urine samples were obtained post mortem.
Ten sheep were anesthetized and mechanically ventilated. Whole lung deposition of nebulized Tc-tobramycin 400 mg was significantly lower than with i.v. (8.8 vs 57.1%, p<0.001). For both administration routes, upper lung zones had a significantly lower deposition than the rest of the lungs. Dorsal deposition was significantly higher with nebulized Tc-tobramycin 400 mg compared to i.v. (68.9 vs 58.9%, p=0.003). The lung concentrations of Tc-tobramycin were higher with i.v. compared to nebulized. There were significantly higher concentrations of Tc-tobramycin in blood, liver and urine with i.v. administration compared to nebulized.
Nebulization resulted in lower whole and regional lung deposition of Tc-tobramycin and also appears associated with low blood and extra-pulmonary organ concentrations.

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