Safety, Tolerability, and Clinical Effectiveness of Adapalene/Clindamycin Phosphate Gel (Klenzit®-C) in Vietnamese Patients With Mild to Moderate Acne Vulgaris

Acne vulgaris is a chronic, multifactorial inflammatory skin disease and one of the most common conditions treated by dermatologists. Its development involves abnormal follicular keratinization leading to microcomedone formation, increased sebum production, colonization by Cutibacterium (Propionibacterium) acnes, and inflammation. Topical retinoids are recommended as first-line therapy for both inflammatory and non-inflammatory acne. Combining a retinoid with a topical antibiotic targets several of these pathways at once and has shown greater and faster efficacy than either agent alone in published studies.

Adapalene is a synthetic naphthoic acid derivative with retinoid activity. It acts through nuclear retinoic acid receptors to normalize follicular epithelial differentiation and has anti-inflammatory effects. Clindamycin phosphate is a lincosamide antibiotic that inhibits bacterial protein synthesis and is bactericidal against C. acnes. Adapalene's action on microcomedone formation may also reduce the selective pressure for antibiotic resistance compared with clindamycin monotherapy.

Klenzit®-C gel (adapalene 1 mg/g and clindamycin 10 mg/g) has been approved in Vietnam since 26 May 2008. Periodic Safety Update Reports covering 2015-2024 identified no new or significant safety signals. Reported events were mainly application-site and skin reactions, along with hypersensitivity reactions such as angioedema and swelling of the face or lips.

Regulatory Context The Ministry of Health of Vietnam, through the Drug Administration of Vietnam (DAV), has asked for continued clinical data on the product's safety and effectiveness. The study is conducted under Circular 12/2025/TT-BYT (16 May 2025) of the Ministry of Health. It also references the DAV meeting minutes on the product's registration number (Wave 111, 28 October 2022 and 02 November 2022).

Enrollment and Study Procedures Patients give written informed consent, or assent with guardian consent for minors, before any study procedure. Each participant receives a unique identification number. Women of childbearing potential have a pregnancy test before enrollment. The first application of the gel is done in the clinic at the baseline visit.

At each visit, the investigator records vital signs (temperature, blood pressure, heart rate, respiratory rate), height, weight, BMI, adverse events, skin tolerability, and concomitant medications. Lesion counts, IGA scoring, and standardized clinical photography are done at baseline and at Weeks 4, 8, and 12. The photographs are kept as confidential study data.

Participants may use gentle cleansers, moisturizers suited to their skin type, and sunscreen. Other topical medications are not permitted. This includes topical retinoids, anti-inflammatories, antimicrobials, and corticosteroids, as well as medicated cleansers, medicated moisturizers, and skincare products containing active ingredients such as salicylic acid, benzoyl peroxide, azelaic acid, niacinamide, AHAs, or retinol.

Participants are withdrawn if they use prohibited topical products, need a temporary dose reduction (for example, applying every other day), become pregnant, or have an intolerable adverse event. The investigator may also withdraw a participant at their discretion. Withdrawn participants are not replaced.

Assessment Scales and Definitions

Investigator Global Assessment (IGA): a 6-point scale (0 = clear, 1 = almost clear, 2 = mild, 3 = moderate, 4 = severe, 5 = very severe). Treatment success means an IGA of 0 or 1 together with at least a 2-grade improvement from baseline.

Local skin tolerability: erythema, dryness, hyperpigmentation, peeling, and pruritus, each graded on a 4-point scale (0 = none, 1 = mild, 2 = moderate, 3 = severe).

Acne purging vs. breakout: to keep adverse event reporting consistent, purging is defined as a temporary rise in comedones of 30% or more with a rise in inflammatory lesions of 25% or less. It typically occurs within weeks 1-4 and resolves within about 8 weeks. A breakout (flare) is defined as a rise in inflammatory lesions of more than 50%, possibly with nodules or spread to new areas.

Safety Monitoring Adverse events are collected from consent through the end of follow-up and coded using MedDRA. Severity is graded as mild, moderate, or severe, and relationship to the study drug as related or not related. Serious adverse events and pregnancies are reported to the sponsor within 24 hours. The interim safety review covers adverse events, serious adverse events, and skin tolerability data.