Final answer:
The 20-year-old with cystic acne who has tried multiple treatments to no avail is the best candidate for isotretinoin therapy. This severe form of acne can lead to scarring, and isotretinoin is a potent medication used when other treatments fail.
Step-by-step explanation:
The best candidate for isotretinoin therapy among the options provided is the 20-year-old patient with cystic lesions who has tried various therapies with minimal effect. Isotretinoin is a powerful medication reserved for severe acne cases that have not responded well to other treatments. Since the 17-year-old has not yet tried antibiotics or hormonal therapies, which are typically indicated before isotretinoin, and the 18-year-old is seeing improvement with Tretinoin, they are less suitable candidates. The 14-year-old with a family history of ice pick scars might be considered for isotretinoin due to the potential for scarring; however, the presence of only open and closed comedones suggests that milder treatments could still be effective. The 20-year-old's lack of response to multiple therapies and the presence of cystic lesions, which carry a high risk of scarring, make isotretinoin the most indicated treatment in this case.
Propionibacterium acnes plays a role in the development of acne by contributing to the infection and inflammation that can lead to redness and scarring. Treatment options for acne range from over-the-counter products with salicylic acid or benzoyl peroxide for mild cases to antibiotics, hormones, and ultimately isotretinoin for more severe cases.