Allergies occur when your immune system reacts to a foreign body. Foreign body may medicine like oxycodone, pollen, animal dander, dust and insect venom etc. When you have allergies, your immune system makes antibodies that identify a particular allergen as harmful, even though it isn t. When you come into contact with the allergen, your immune system s reaction can inflame your skin, sinuses, airways or digestive system. The severity of allergies varies from person to person and can range from minor rash to anaphylaxis — a potentially life-threatening emergency Advice 1. Stop oxycodone immediately. Do not take it future also. Always keep a card in your pocket mentioning that you have allergy to oxycodone. 2. Tablet levocetirizine 5 mg – 1 tablet once daily for 5 days 3. Tablet dexamethasone (Dexona) 0.5 mg – 1 tablet twice daily for 5 days 4. Do not scratch too much as it will caused skin damage and infection 5. You can apply calamine lotion – three times daily – will provide soothing effect 6. Immediately go to hospital if you have any sign of anaphylaxis such as breathing difficulty, low blood pressure, nausea/vomiting, throat constriction, unconsciousness etc Thanks!