IN-VITRO ASSESSMENT OF DRUG-DELIVERY THROUGH AN ENDOTRACHEAL-TUBE USING A DRY POWDER INHALER DELIVERY SYSTEM

Background - Jet nubulisers and metered dose inhalers are widely used to deliver aerosolised drugs to the lungs of intubated patients in adu lt intensive care units. Drug delivery using these systems has been sh own to be inefficient and both forms of delivery have the potential to induce paradoxical bronchoconstriction in patients with reactive airw ays disease. Methods - Experiments were carried out to determine wheth er it was possible to deliver drug from a dry powder delivery system t hrough an endotracheal tube. A 200 mu g budesonide Turbohaler was encl osed in a chamber which allowed it to be inserted into a ventilator ci rcuit. Experiments were performed with a multistage liquid impinger in which drug was drawn through the Turbohaler and endotracheal tube at 60 l/min providing an index of the maximum drug delivery achievable vi a this route. A second series of experiments was performed in which th e Turbohaler was placed in a ventilator circuit using a Servo 900C vol ume cycled ventilator. Drug delivered from the Turbohaler during the i nspiratory phase was collected on a filter placed between the end of a 9 mm endotracheal tube and a model lung. A tidal volume of 500 ml and inspiratory time of 0.5 seconds was used. Budesonide was assayed usin g an ultraviolet spectrophotometric assay. Results - Thirty percent of the nominal dose passed through the endotracheal tube and was collect ed in the multistage liquid impinger. Mean drug delivery to the filter in the ventilator circuit was 20%. Conclusions - This in vitro study indicates that drugs from dry powder inhalers (in this case the Turboh aler) can be satisfactorily delivered through endotracheal tubes and t hat clinical evaluation of this technique is now indicated.