Doxycycline vs. Macrolide for MRMP (DOMINO)

Inclusion Criteria: * Age: 3 to 17 years at the time of enrollment. * Diagnosis: Clinically diagnosed CAP characterized by respiratory symptoms (e.g., fever, cough, auscultatory findings) and chest X-ray confirming pulmonary infiltrates. * Pathogen: Confirmed MP M. pneumoniae infection via PCR OR strongly suspected infection based on clinical features and epidemiological grounds (e.g., outbreaks among classmates, poor response to prior non-macrolide antibiotics). * Resistance: Suspected macrolide-resistant M. pneumoniae (MRMP) infection (e.g., during a reported local epidemic of MRMP). * Timing: Ability to register and initiate the study drug within 72 hours of symptom onset. Exclusion Criteria: * Prior use of tetracyclines, macrolides, or quinolones for the current illness. * Complicated pneumonia (e.g., necrosis, empyema, lung abscess) or severe pneumonia requiring immediate intensive care or exhibiting hypoxia (SpO₂ \<90%). * Hypersensitivity or contraindications to macrolides or tetracyclines. * Severe immunocompromised state or severe underlying lung disease. * Severe hepatic impairment (AST/ALT \>3x upper limits) or severe renal impairment.