Longitudinal analysis of FEV1 changes related to antibiotic therapy in children with cystic fibrosis.

The measurement of FEV1 in children with cystic fibrosis has been shown to be the most important objective measurement for survival. It has been observed that children receiving intravenous antibiotics usually show a significant improvement in FEV1 with therapy in the short term. We hypothesized that the FEV1 measured pre-antibiotic therapy and followed longitudinally would show a greater rate of decline and may be a better prognostic indicator than the FEV1 post antibiotic therapy. The study cohort consisted of 60 children with cystic fibrosis who attended the St. James' Hospital cystic fibrosis unit between 1993 and 1999. Mixed model regression analysis provided estimates of the average rate of change of the pre-FEV1, post-FEV1 and FEV1 difference in subgroups based on survival, sex and pseudomonas status. There was no significant difference seen in the rate of decline of the FEV1 difference when comparing those who died and those who survived (p = 0.93). This was also the case when males were compared to females (p = 0.09). Both pre-antibiotic FEV1 and post-antibiotic FEV1 measurements showed a significant difference in rate of decline when comparing those who died (FEV1 slope = -6.4, -6.3) to those who survived (FEV1 slope = -1.9, -1.7) [p = 0.001, p = 0.0005] and when males (FEV1 slope = -0.6, -0.03) were compared to females (FEV1 slope = -3.3, -3.5) [p = 0.03, p = 0.002]. Our study demonstrated that there was no additional value in measuring FEV1 pre-antibiotic therapy compared to the FEV1 post antibiotic therapy in improving the sensitivity of FEV1 as a marker of decline. This study confirms that the rate of decline in FEV1 is a strong predictor of mortality and that females in this age group decline faster than their male counterparts.