Can Flucloxacillin be used when you have VERY bad cold-sores all around your mouth?

Flucloxacillin is an antibiotic that is not used to treat cold sores/ fever blisters. Cold sores are caused by the herpes simplex virus, and antibiotics only work against bacteria.

Antiviral medications, such as acyclovir, valacyclovir, or famciclovir are the treatments of choice for cold sores.