Purpose <p>Circadian rhythms regulate key physiological processes, including metabolism, immune function, and organ perfusion, which can influence antimicrobial pharmacokinetics and, in turn, may indirectly shape pharmacodynamic outcomes through changes in drug exposure or host immune responses. This review examines the evidence supporting circadian effects on antimicrobial efficacy and toxicity and evaluates the potential clinical relevance of time-of-day dosing.</p> Methods <p>We conducted a narrative review of 84 experimental and clinical studies published up to November 2025, identified through PubMed and Scopus. Eligible studies evaluated time-of-day or circadian effects on antimicrobial pharmacokinetics, safety, efficacy, or host immune response across major antibacterial, antiviral, antifungal, and antiparasitic drug classes.</p> Results <p>Circadian variation in gastric motility, hepatic metabolism, and renal clearance can alter antimicrobial exposure independent of dose. The most consistent circadian associations relate to toxicity: aminoglycoside and amphotericin B nephrotoxicity are more frequent with rest-phase dosing, while fluoroquinolone-associated QT prolongation is greater with afternoon administration, suggesting a relative safety advantage with morning dosing. Evidence for circadian modulation of antimicrobial efficacy is limited and heterogeneous, with observed effects more plausibly explained by variations in drug exposure, host immunity, or particularly in parasitic infections-pathogen developmental stage rather than intrinsic circadian changes in pathogen susceptibility. For many antivirals and antifungals, long half-lives and fixed dosing schedules minimize the clinical impact of dosing time.</p> Conclusion <p>Overall, circadian regulation may influence antimicrobial pharmacology and toxicity in selected settings, although the available evidence is heterogeneous and clinical validation remains limited.</p>