Reviving Old Antibiotics: New Indications and Therapeutic Perspectives—A Review

The rapid global spread of antimicrobial resistance (AMR) has significantly reduced the effectiveness of many modern antibiotics, creating an urgent need for alternative therapeutic strategies. One promising approach is the revival and repurposing of older antimicrobial agents whose clinical potential was previously limited by toxicity concerns, pharmacokinetic challenges, or the availability of newer drugs. Recent advances in drug delivery, dosing optimization, and antimicrobial stewardship have renewed interest in these compounds as viable options for the treatment of multidrug-resistant infections. The aim of this review is to provide a comparative, clinically oriented analysis of selected "old" antibiotics, fosfomycin, colistin, streptomycin, and vancomycin, with emphasis on their current therapeutic roles, pharmacokinetic/pharmacodynamic (PK/PD) targets, toxicity mitigation strategies, resistance mechanisms, and evidence supporting combination therapies and alternative routes of administration. This narrative review was conducted using a structured PubMed search and manual reference screening, focusing on clinical, PK/PD, and translational studies relevant to the contemporary use of legacy antibiotics. The review summarises current evidence on the re-emerging clinical applications of these agents, each discussed in the context of historical use, mechanism of action, resistance patterns, and newly identified indications. Attention is given to novel formulations, combination strategies, and alternative routes of administration that enhance efficacy while limiting toxicity, including applications in biofilm-associated infections. Overall, strategic repurposing of older antibiotics represents a valuable complementary approach in the fight against AMR and may extend the therapeutic lifespan of existing agents in an era of limited antibiotic innovation.