The purpose of this study is to evaluate, at steady-state, the systemic exposure and the lung deposition of B17MP (active metabolite of BDP) as AUC0-12h,ss and Cmax,ss, after inhalation of BDP (Clenil® Modulite®) with the AeroChamber Plus™ spacer device or with the Volumatic™ spacer device without or with charcoal block.

Inclusion Criteria:

• Male or non-pregnant female patients aged 18-65 years included.
• Diagnosis of asthma according to GINA guidelines 2009 made at least 6 months prior to screening.
• Patients already treated with a dose of BDP or equivalent up to 2000 µg/day.
• FEV1 ≥ 60% of predicted for the patient's normal value at screening and randomisation

Exclusion Criteria:

• Patients treated with oral or parenteral corticosteroids in the previous 8 weeks (12 weeks for parenteral depot corticosteroids) before screening visit.
• Exacerbation of asthma symptoms or hospitalization due to asthma exacerbation within the previous one month before screening until randomisation.
• Lower respiratory tract infection within one month prior to screening.
• Diagnosis of COPD as defined by the current GOLD 2009 (Global Initiative for Chronic Obstructive Lung Disease) Guidelines.
• Significant medical history and/or treatments for cardiac, renal, neurological, hepatic, endocrine diseases, or any laboratory abnormality indicative of a significant underlying condition, that may interfere with patient's safety, compliance, or study evaluations, according to the Investigator's opinion.
• Treatment with a xanthine derivative (e.g. theophylline) formulation in the 4 weeks prior to screening.
• Any enzyme inducing or inhibiting drug (from 8 weeks before screening visit)
• Patients who received any investigational new drug within the last 8 weeks before the screening. The patients cannot participate in another clinical study at the same time as the present study.
• Blood donation (450 mL or more)or significant blood loss less than 12 weeks before the first intake of study drug.