Background: Antibiotic resistance in Cystic Fibrosis (CF) patients has been a serious issue in their survival. The objective of this study was to investigate the antibiogram trend in serial admissions among CF patients.
Materials and Methods: In this retrospective descriptive-analytical study, from 2014 to 2019, 95 known cases of CF patients with repeated admissions at Masih Daneshvari Hospital, Tehran, Iran, were evaluated. Demographic data and para-clinical parameters were evaluated. Fourteen antibiotic disks were used to determine antibiotic resistance. Resistance trend in 2014 and 2018 was compared.
Results: Out of 95 patients, 48 patients (52.2%) were female. The mean age of patients was 19.43 ± 6.7 years. Pseudomonas positive culture in the first admission was 68.4%; while it was 45.3% in the second admission and 28.4% in the third admission (p> 0.05). Staph positive culture was 20%; 18.9%, and 16.8%, respectively (p> 0.05). Pseudomonas aeruginosa was the most sensitive to vancomycin (93.8%), followed by colistin (93.3%) and ceftazidime (65.2%). There was no correlation between patients' age and multidrug resistance (MDR). FEV1 was significantly lower in both the patient with positive pseudomonas (p-value: 0.01), and culture and MDR (p= 0.023). Furthermore, in terms of antibiotic resistance over time, resistance to colistin statistically decreased from 25% in 2014 to 2% in 2018 (p= 0.02). 
Conclusion: Vancomycin, Colistin, Ceftazidim, Imipenem, Amikacin, and Gentamycin had the highest drug sensitivity; while Cefotaxime, Clindamycin, and Chloramphenicol antibiotics had a low sensitivity. From 2014 to 2019, resistance to Colistin dramatically decreased.