Hello, Discoloration of teeth is not a common side effect for this antibiotic. Tetracylcine given before age 8 is a well known antibiotic that can cause yellowing or dark bands to form in the underneth layer of a tooth. Flucloxacillin is not in the same family of antibiotics. If you notice a coating on your daughter s teeth, see if this can be removed by proper cleaning. I would suggest a dental exam and dental office cleaning if you are unable to remove the film. A secondary infection can occur in the mouth leaving a white film on the tongue. The gums will often be sore and red in appearance. This would be oral thrush and can be treated by your dentist. Antibiotic treatment can cause an imbalance of the natural bacteria and an excess of certain bacteria can take over. A change in the color of the gums could make the teeth appear a different color as well. Are these adult front teeth or still baby teeth that you are concerned about? Are there any other medical concerns or medications being taken? Yellowing of the skin or eyes indicates a complication with the liver that would need to be addressed by your physician. Teeth are made up of tubules with the center pulp containing blood vessels and nerves. This layer is what mainly affects the color of the tooth and could exhibit a transient change. Teeth subject to trauma or root canal can darken from the inside. Changes to the outer layer of enamel such as decalcification, decay and too much flouride can cause a color change. I am trying to cover some situations that may be possible from your description. I would be happy to answer any additional questions with more details. Having your daughter make a visit to the dentist would give you the best answer and allow necessary treatment.