Review on transdermal patches: optimization in drug administration.

Aim: To synthesize technical, clinical, and regulatory knowledge on transdermal patches and identify persistent gaps that impact their safe and effective use. Methods: Data sources and selection criteria were defined as follows. Sources consulted included PubMed, Scopus, ScienceDirect, and Google Scholar; regulatory agency websites (FDA, EMA, ANVISA, INVIMA); and official pharmacopeial and methodological documents (USP-NF, European Pharmacopoeia, OECD). English, Spanish, and Portuguese sources were considered, with no predefined time limits. The last search update was performed on September 9, 2025. Regarding study selection, the narrative approach includes published reviews, relevant primary studies, official regulatory guidance's/Q&A, and pharmacopeia standards related to design, release/permeation, bioavailability/bioequivalence, adhesion, and regulatory frameworks. Non-authoritative or commercial webpages and duplicates were excluded, with priority given to official and peer-reviewed sources. This review was appraised against the SANRA criteria, covering justification of the article's importance, statement of aims, description of the literature search, referencing, scientific reasoning, and appropriate presentation of data. Results: Transdermal systems may offer sustained drug delivery and adherence advantages, but their real-world performance is constrained by biological variability, patient misuse, and fragmented regulatory requirements. Adhesion remains a critical quality attribute, yet test methods are heterogeneous and alignment between Conclusions: Stronger harmonization of adhesion and bioequivalence standards, together with improved patient education and testing under real-life stress conditions, is needed to ensure the quality, safety, and interchangeability of innovator and generic transdermal products.