This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Acne and chemical peeling, Subject name: Dental
Recalcitrant acne is treated by: 
Select and explain. 
A. Oral erythromycin, B. Oral tetracycline, C. Retinoids, D. Steroids
C: Retinoids
Answer: C: Retinoids 
Explanation: The European S3 guidelines recommend isotretinoin for the treatment of severe recalcitrant acne or moderate acne that has failed to respond to conventional antibiotic therapies. Retinoids - Isotretinoin : D.O.C for severe / gd 4 / nodulocystic acne/ acne conglobata. Dose 0.5 - 1 mg / kg body weight to be given till cumulative dose of 120-150mg/kg body weight.