Drug Repurposing: Strategies, Methodologies, and Emerging Therapeutic Innovations

Drug repurposing, also referred to as drug repositioning or therapeutic switching, is a
strategic approach aimed at identifying novel therapeutic indications for existing drugs,
including approved, investigational, or discontinued molecules. Conventional drug discovery
is associated with prolonged development timelines, high research and development costs,
and significant failure rates, particularly during late-stage clinical trials. Drug repurposing
addresses these challenges by leveraging prior knowledge of pharmacokinetics, safety,
toxicity, and manufacturing processes, thereby substantially reducing development time and
economic burden. The present chapter provides a structured and comprehensive overview of
drug repurposing based on well-established strategies and methodologies. The introduction
outlines the rationale and growing importance of repurposing in modern pharmaceutical
sciences. The methods section, derived from established conceptual frameworks, describes
on-target and off-target repurposing strategies, experimental and in-silico approaches,
methodological classifications, and key databases used in the repurposing process. Recent
advances, including artificial intelligence, network pharmacology, and multi-omics
integration, are incorporated to reflect current trends. This chapter emphasizes drug
repurposing as a rational, efficient, and sustainable approach to accelerate therapeutic
innovation and address unmet medical needs.