What medication is commonly prescribed for severe acne vulgaris?

Isotretinoin is commonly prescribed for severe acne vulgaris because it is a powerful retinoid that targets the underlying causes of acne, including excess sebum production, abnormal keratinization, and inflammation. It works by reducing the size and activity of sebaceous glands, leading to a significant decrease in oiliness and the formation of new acne lesions. Additionally, isotretinoin has anti-inflammatory properties that help to reduce the redness and swelling associated with acne.

This medication is typically used when other treatments, such as topical agents and oral antibiotics, have failed to produce adequate results. Due to its potency, isotretinoin can lead to significant improvements in severe cases of acne and is often viewed as a last resort therapy for patients with resistant or cystic acne.

The other medications listed serve different purposes: Acyclovir is an antiviral used for viral infections, ketoconazole is an antifungal, and ethambutol is an antitubercular agent. None of these directly address the causes or treatment of severe acne vulgaris.