Study to Investigate the Effect of PBF-680 on Forced Expiratory Volume in 1 Second (FEV1) in Asthmatic Patients

Inclusion Criteria: * Written informed consent must be obtained before any study assessments are performed. Subjects must be able to communicate well with the investigator and staff so that they can understand and comply with the requirements of the study. * Male and female subjects of 18-65 years age. * Subjects with a medical history of mild-to-moderate persistent allergic asthma, diagnosed according to GINA 2017 guidelines, and managed in therapeutic steps 2-3 being inhaled corticosteroid (ICS) limited to low/medium dose, or step 4 restricted to medium-dose ICS plus ong-acting beta2-agonist (LABA) and/or a leukotriene antagonist, as maintenance therapy. * A positive skin prick test to aeroallergens, such as house dust mite, tree or grass pollen, pet dander, or cockroach antigens. In addition, any allergens specific to the country/locality can be included. * Women of child-bearing potential must agree to employ effective contraception from Visit 1 through FU visit, unless they are surgically sterile (i.e. bilateral tubal ligation, bilateral oophorectomy, or complete hysterectomy), are at least 2 years postmenopausal, or practice abstinence. * All female subjects must have negative pregnancy test results at screening and baseline. * Male subjects must agree to use two acceptable methods of contraception, (e.g. spermicidal gel plus condom) for the entire duration of the study and up to the study completion visit, and refrain from fathering a child within the three months follow…