Thanks for posting your question on HCM!
I appreciate your concern regarding the safety of Flucloxacillin.
Presence of food in the stomach interferes with the absorption of Flucloxacillin hence maximum absorption occurs on empty stomach and found to be more efficient.
Since you are going to take this antibiotic for a shorter interval of time, the heart burn as such will not cause any problem because once you complete your course of antibiotic, the heart burn also subsides.
The heart burn can be prevented by use of
Ranitidine or
Omeprazole but either of these two medications should not be taken along with Flucloxacillin.
Ranitidine or Omeprazole can be taken 1-2 hrs after having meals with before meal intake of Flucloxacillin.
If you really need a pain killer either Ranitidine or Omeprazole will prevent its side effects of heart burn and other acidity related stomach problems.
I hope your doubts have been clarified.
Take care of your health.