The goal of this clinical trial is to learn if doxycycline works to treat pneumonia in children. It focuses on children with Mycoplasma pneumoniae infection that may not respond to standard medicines. The main questions it aims to answer are:

• Does doxycycline stop fevers faster than azithromycin?
• Is doxycycline safe for children, specifically regarding tooth color changes?

Researchers will compare doxycycline to azithromycin to see if doxycycline works better to treat this type of pneumonia.

Participants will:

• Take either doxycycline or azithromycin by mouth for 7 to 14 days.
• Check their body temperature to see when their fever goes away.
• Visit the hospital to check for any medical problems.
• Have their teeth checked for color changes 28 days after starting the medicine.

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.

De-identified individual participant data (IPD) that underlie the results reported in the publication will be made available to researchers who provide a methodologically sound proposal. This includes text, tables, figures, and appendices. IPD will be available beginning 6 months and ending 36 months following article publication.

Supporting Information: The study protocol, statistical analysis plan (SAP), and informed consent form will also be shared. Access Criteria: Proposals should be directed to the Principal Investigator at [Insert Official Email Address]. To gain access, data requestors will need to sign a data access agreement.