- Must demonstrate a dual airway response to an allergen challenge in Period 1, decrease in FEV1 of at least 20% 0 to 2 hours after allergen challenge for early asthmatic response (EAR) and a positive late asthmatic response (LAR) to an inhaled allergen challenge as defined by a bronchoconstrictive response of at least 15% reduction in FEV1 3 to 8 hours after allergen challenge