Accutane. Antibiotic can suppress cystic acne but once stopped the acne will return. If the acne is extensive and persistent the best alternative may be accutane, which needs to be pressings by a dermatologist experienced with the drugs use. Careful monitoring to prevent prevent pregnancy for one month prior and two months after a 15-20 week course is essential.
Many options. Using topical meds like benzoyl peroxide, Erythromycin or Clindamycin gel, sulfacetamide, and washes containing glycolic or salicylic acid can help. If that doesn't clear it up then you may need oral antibiotics such as doxycycline, or minocycline. For severe cases not responsive to anything else then isotretinoinsy be the last resort.