Doxycycline for Macrolide-Resistant<em> Mycoplasma pneumoniae</em> Pneumonia in Children: Analysis of Efficacy and Safety Across Different Age Groups

[Objective]: The objective is to assess the effectiveness and safety of doxycycline for treating macrolide-resistant Mycoplasma pneumoniae pneumonia (MRMPP) in pediatric patients across various age ranges, and to explore the value of early switching to doxycycline therapy in children aged &lt;8 years. [Methods] This retrospective cohort study included children diagnosed with MRMPP due to mutations in the 23S rRNA V domain confirmed by sputum PCR, admitted to our hospital from January 2023 to April 2024. The children were grouped by age and treatment regimen: Children aged ≥8 years were divided into the oral doxycycline treatment group (DX group) and the intravenous azithromycin treatment group (AZ1 group); Children aged &lt;8 years were divided into the azithromycin-to-doxycycline switching group (AD group, further subdivided into subgroup AD1 [switching time ≤3 days] and subgroup AD2 [switching time &gt;3 days]) and the intravenous azithromycin group (AZ2 group). The length of hospital stay, duration of fever, time to cough relief, rate of imaging improvement, and adverse drug reactions were compared among the groups. [Results] A total of 173 patients were included, with 42 patients aged ≥8 years (DX group: 27 cases, AZ1 group: 15 cases) and 131 patients aged &lt;8 years (AD group: 52 cases, including AD1 group: 22 cases, AD2 group: 30 cases; AZ2 group: 79 cases). For patients aged ≥8 years, those in the DX group experienced a markedly reduced duration of hospitalization when compared to the AZ1 group (7.11±1.78 days vs. 8.33±0.97 days, P=0.007). Furthermore, the DX group had a shorter period of fever (3.37±1.18 days vs. 4.33±0.72 days, P=0.011) and achieved cough relief more quickly (5.96±1.76 days vs. 7.33±0.97 days, P=0.008). Additionally, the rate of improvement seen in imaging results was greater in the DX group (63.0% vs. 20.0%, P=0.011), and the length of time for glucocorticoid treatment was reduced (2.15±1.81 days vs. 4.07±2.49 days, P=0.013). For patients aged &lt;8 years, the AD group had a shorter hospital stay compared to the AZ2 group (8.12±1.56 days vs. 8.76±1.75 days, P=0.029) and a faster resolution of fever (3.85±1.60 days vs. 4.65±1.51 days, P=0.005). Analysis of subgroups showed that the efficacy metrics for the AD1 group outperformed those of the AD2 group (P&lt;0.05). In the cohort of severe patients (aged &lt;8 years): the ADsp group (n=27) experienced notably shorter hospital stays (9.04±1.61 days vs. 10.93±1.34 days, P&lt;0.001), a reduced duration of fever (4.52±1.87 days vs. 5.73±1.58 days, P=0.032), and a decreased incidence of glucocorticoid administration (74.1% vs. 100%, P=0.038) relative to the AZ2sp group (n=15). Regarding safety, the doxycycline group experienced mild adverse reactions (1 case of vomiting in the ≥8 years group and 2 cases of rash in the &lt;8 years group), which were alleviated after symptomatic treatment, demonstrating good tolerance. [Conclusion] Doxycycline is effective and safe for treating pediatric MRMPP. It can be used as a first-line initial treatment for patients ≥8 years old. For patients &lt;8 years old who do not respond to azithromycin within 72 hours (especially severe cases), switching to doxycycline early is beneficial for shortening the disease course and reducing the risk of complications.