The rise of drug-resistant organisms and the need to minimize side effects calls for a new approach to antibiotic therapy duration. This study explores tailoring the length of antibiotic treatment to patient recovery, focusing on whether adjusting therapy based on when the patient feels better is as effective as completing the prescribed course for acute respiratory tract infections (RTIs). The investigators will enroll 474 outpatients aged 18-75 with acute RTIs across 25 Spanish healthcare centers. Patients will be randomized into two groups: one following standard full-course antibiotic therapy, and another receiving a tailored approach, where treatment may be shortened based on clinical assessments. The primary outcome is clinical efficacy at day 14. Secondary outcomes include antibiotic duration, complications, and quality of life.