iFAAM: The Impact of Proton-pump Inhibitors (Antacids) on Threshold Dose Distributions

Inclusion Criteria: * signed informed consent, history of walnut allergy,minimum age 18 years Exclusion Criteria: * • Known hypersensitivity or allergy to Omeprazole, other proton pump inhibitors, mannitol, ingredients of placebo meal * Drugs not allowed during the study due to proved interaction with Omeprazole: Digoxin, Clopidogrel, Methotrexate, Antiretroviral drugs, Diazepam, Cilostazol, Phenytoin, Warfarin (R-Warfarin) and other Vitamin K antagonists, Phenytoin, Tacrolimus, Clarithromycin, voriconazole, Rifampicin and Hypericum * Drugs not allowed due to interference with the food challenge (or shortest interval between last treatment and food challenge) * corticosteroids systemically (2 weeks) * antihistamines (3 days) except hydroxyzine (10 days) * ketotifen (2 weeks) * betablocker (1 day) * angiotensin converting enzyme (ACE) inhibitors (2 days) * omalizumab (2 months) * Women who are pregnant or breast feeding * Intention to become pregnant during the course of the study * Lack of safe contraception, defined as: female participants of childbearing potential, not using and not willing to continue using a medically reliable method of contraception for the entire study duration, such as oral, injectable, or implantable contraceptives, or intrauterine contraceptive devices * Please note that female participants who are surgically sterilised / hysterectomised or post-menopausal for longer than 2 years are not considered as being of child bearing potential. * Uncontrolled asthma, forced expiratory volume \<70% predicted value * Acute allergic disease * Chronic urticaria * Mastocytosis * Other clinically significant concomitant disease states (major organic or infectious diseases, e.g., renal failure, hepatic dysfunction, cardiovascular disease, acute febrile infection), * Known or suspected non-compliance, drug or alcohol abuse, * Inability to follow the procedures of the study, e.g. due to language problems, psychological disorders, dementia, etc. of the participant, * Participation in another study with investigational drug within the 30 days preceding and during the present study