In asthma, breathing in an allergen, such as house dust mite induces inflammation in the airways. This process appears to involve an interaction between two different sorts of blood cells, platelets and white blood cells via a receptor called the P2Y12 receptor. The purpose of this study is to determine whether the drug clopidogrel which blocks the P2Y12 receptor on platelets, reduces inflammation following breathing in house dust mite in people with mild asthma.

Inclusion Criteria:

• Confirmed diagnosis of asthma
• Step one of treatment by GINA (2006) guidelines
• baseline FEV1 >80% predicted

Exclusion Criteria:

• current smoker
• ex smoker who quit <1 year prior to study and pack history >10 pack years
• current use of aspirin or other anticoagulant medication
• Diagnosis or documented history of bronchopulmonary aspergillosis or uncontrolled infections
• Any clinically significant cardiopulmonary abnormalities not related to pre-existing asthma
• Past or present tuberculosis, systemic lupus erythematosis or multiple sclerosis
• Any clinically significant neurological, renal, endocrine, gastrointestinal, hepatic or haematological abnormalities uncontrolled with standard treatment
• History of psychiatric, medical or surgical disorders that may interfere with study
• Clinical history suggestive of respiratory infection in month preceding study
• Alcohol or recreational drug abuse
• Diagnosis of immunodeficiency requiring treatment
• Treatment with immunomodulators (inhaled corticosteroids in two months or oral corticosteroids in six months prior to study)
• Ongoing allergen desensitisation therapy
• Regular use of sedatives, hypnotics, tranquillisers
• Positive hepatitis viral antigens or antibodies
• Blood donation within 3 months of the study
• Live immunisation <4 wks prior to study
• Inability to understand directions for study assessment
• Inability to be contacted in case of emergency
• Participation in another study at the same time or within a prior 3-month period