Abstract: OBJECTIVE To observe the effect of antibiotics de-escalation regimen on pulmonary ventilation function and serum inflammatory cytokines of patients with severe lower respiratory tract infections. METHODS A total of 68 patients with severe lower respiratory tract infections who were treated in internal medicine department from Jan 2016 to Jan 2017 were enrolled in the study and randomly divided into the control group and the experimental group, with 34 cases in each group.The experimental group was given intravenous drip of 0.45 g of meropenem plus 100 ml normal saline, once per 6-12 hours, after the continuous treatment for 4 days, the patients were treated with meropenem by reducing the dosage of 0.5-1 g/d or were treated with sensitive antibiotics for 4-12 days.The control group was given intravenous drip of 2g ceftriaxone sodium plus 100 ml normal saline, once daily, with the treatment for 5-12 days in total.The clinical efficacy, respiratory mechanics indexes, serum inflammatory cytokines, pulmonary function indexes and incidence of adverse reactions were observed and compared between the two groups of patients after the treatment. RESULTS The total effective rate of clinical treatment of the experimental group was 79.41%, significantly higher than 55.88% of the control group (P＜0.05).There was no significant difference in the clinical efficacy, respiratory mechanics indexes, serum inflammatory cytokines or pulmonary function indexes between the two groups of patients before the treatment.The levels of respiratory mechanics indexes PIP, Raw and WOB of the two groups of patients were reduced after the treatment, while the Cdyn level was elevated, the amplitudes of reduced levels of PIP, Raw and WOB of the experimental group were significantly greater than those of the control group, and the amplitude of elevated Cdyn level of the experimental group was greater than that of the control group (P＜0.05).The levels of serum BNP, CRP, IL-6 and PCT of the two groups of patients were reduced after the treatment, while the amplitudes of reduced serum BNP, CRP, IL-6 and PCT of the experimental group were greater than those of the control group (P＜0.05).The FEV1/FVC and FEV1/expected value of the two groups of patients were significantly increased after the treatment, while the FEV1/FVC and FEV1/expected value of the experimental group were increased more remarkably than those of the control group (P＜0.05).There was no significant difference in the incidence of adverse reactions between the two groups of patients. CONCLUSION The antibiotic de-escalation regimen may achieve remarkable clinical effect on the patients with severe lower respiratory tract infections, raise the levels of serum inflammatory cytokines and improve the pulmonary ventilation function, with the drug safety high, and it is worthy to be promoted in the hospital.