Hi there,
This is a common concern of my patients when I discuss with them the use of doxycycline to treat their acne flare. Doxycycline is a common and safe antibiotics that is used to treat moderately severe inflammatory acne. It should be taken for a specific period of 2 to 4 months. Prolonged usage of doxycycline for more than six months especially when the inflamed acne has subsided or to prevent relapses is not recommended. Doxycycline is not commonly prescribed to treat other infections such sorethroat, chest infection, urinary tract infection and boils. Currently, in clinical practice, the use of doxycycline for acne does not have great impact on the effectiveness of other antibiotics given to treat other infections. Nevertheless, it may be prudent to use medications that do not promote antibiotic resistance such as topical benzoyl peroxide and topical retinoids as first line to treat acne.
Hope this addresses your concern!