The influence of orally deposited budesonide on the systemic availability of budesonide after inhalation from a Turbuhaler.

1. The aim of this pharmacokinetic study was to evaluate to what extent oropharyngeal deposition of drug contributes to the systemic availability of budesonide inhaled from a dry powder inhaler (Turbuhaler). 2. The design was a randomized cross-over study in eight children aged 7-13 years. The plasma concentrations of the two epimers of budesonide (22R and 22S) after inhalation of 1 mg budesonide from a Turbuhaler were compared with the plasma concentrations obtained when the absorption of the drug deposited in the oropharynx was blocked by drinking and rinsing the mouth with charcoal before and after the inhalation. 3. The plasma concentrations of budesonide were significantly reduced by the charcoal treatment (P < 0.01) and the area under the time vs plasma concentration curve 0-4 h was significantly reduced from 9.5 to 8.0 mmol l-1 h for 22S (P < 0.01) and from 7.6 to 5.7 mmol l-1 h for 22R (P < 0.01). 4. The plasma concentrations and the AUCs after both Turbuhaler administrations were markedly higher than those obtained in earlier studies using other inhalers suggesting a higher intrapulmonary deposition of drug after Turbuhaler treatment. 5. It is concluded that oropharyngeal deposition of drug accounts for about 20% of the total systemic availability of budesonide inhaled from Turbuhaler. Thus, the main contribution to the system comes from budesonide absorbed in the airways.