Main substance: isotretinoin (Vitamin A derivative) given systemically

Indication: in moderate to severe acne

Mechanism of action: Retinoids normalize keratinization by inhibiting and modulating keratinocytes → ↓ sebum production

Contraindications:- Pregnancy, women of childbearing age without contraception: strong teratogenic effects- Liver disease- Simultaneous tetracycline treatment

Precautions (in all females of childbearing potential)- 1 month before initiating therapy1. A serum/urine pregnancy test2. Two methods of contraception (oral contraceptive therapy + barrier contraception/IUD)- During therapy: monthly pregnancy test and continuous use of two methods of contraception- After completing therapy:1. Continue two methods of contraception for 1 month2. A pregnancy test at the end of 1 month

Side effects:- Dry skin, xerostomia, cheilitis, pruritus- Headaches, arthralgias, alopecia, fatigue

Laboratory tests:- Blood disorders (e.g., anemia)- ↑ Triglycerides, ↓ HDL, ↑ glucose- ↑ AST, ↑ ALT