N-acetylcysteine (NAC) is a synthetic derivative of L-cysteine, known since the mid-20th century as a mucolytic agent and, in recent decades, has attracted attention for its antioxidant and antibiofilm properties. Bacterial biofilms are structured communities of microorganisms enclosed in an extracellular polymeric matrix, which accounts for their markedly increased resistance to antibiotics (up to 1000-fold higher than in planktonic forms) and to the host immune response. According to the literature, up to 65% of infectious agents are associated with biofilm formation, making them a challenging therapeutic target. This review systematizes current data on the molecular mechanisms of the antibiofilm action of NAC, including disruption of matrix proteins and polysaccharides, degradation of extracellular DNA, suppression of the quorum sensing system, and disturbance of bacterial redox homeostasis. Particular attention is given to synergistic combinations of NAC with antibiotics of five major classes; effective concentrations are provided, and the types of interaction are characterized. The results of clinical studies from the last decade are reviewed, demonstrating the potential of NAC as an adjuvant in urinary tract infections, chronic rhinosinusitis, diabetic osteomyelitis, and cystic fibrosis. The main limitations (pH dependence, instability, low oral bioavailability) are critically evaluated, and approaches to overcoming them using nanoparticles, hydrogels, and combinations with propolis or chitosan are proposed. The review is intended for researchers in antimicrobial chemotherapy and developers of new drug delivery systems.

Acute otitis media is an inflammatory disease affecting all compartments of the middle ear, characterized by localized pain, fever, hearing impairment, and, occasionally, purulent exudate. It represents a significant clinical concern in both pediatric and adult populations, with approximately 709 million cases reported annually worldwide, 51% of which occur in children. However, currently available topical otic formulations are limited by their inability to achieve predictable therapeutic concentrations at the site of inflammation, resulting in reduced efficacy. In addition, the selection of appropriate active pharmaceutical ingredients (APIs) for drug products remains challenging; as a result, existing therapies do not comprehensively address all stages of pathogenesis. This study aimed to analyze existing locally acting formulations for middle ear drug delivery, evaluate their advantages and limitations, and assess modern approaches to the development of novel drug delivery systems and API combinations. A critical review of 69 publications (2010–2026) was conducted, supplemented by a strengths and limitations analysis of dosage forms and an evaluation of APIs based on clinical data. The findings highlight a lack of targeted drug delivery systems, limited efficacy of existing API combinations against bacterial biofilms, and their risk of ototoxicity. Emerging innovative drug delivery approaches, including microemulsions, vesicular systems, stimuli-responsive systems, and hydrogels, have demonstrated promising results in preclinical studies; however, their efficacy and safety remain to be confirmed in clinical settings before their full therapeutic potential in otitis media treatment can be realized.