Hi.. Welcome to HEALTHCARE MAGIC.. I have gone through your query and can understand your concerns.. As per your complain Flucloxacillin is an antibiotic of Penicillin group and at times antibiotics can cause hyperacidity and acid reflux.. Heartburn in your case seems to be due to side effect of antibiotic only and other thing is that you should not take antibiotic on an empty stomach.. I would suggest you not to take Flucloxacillin on empty stomach.. You should take it after meals.. Along with it you can take Calcium Carbonate that is an antacid half an hour before meals... You can also take Proton pump inhibitor like Omeprazole empty stomach in the morning till the time you are on antibiotics as it will help in reducing acid content.. You should also avoid spicy meals.. Drink plenty of water.. Take more of Probiotics like Yoghurt in diet.. In case if there is still no improvement consult your treating physician and get evaluated. Hope this information helps.. Thanks and regards. Dr.Honey Nandwani Arora.