Canada Pharmacy: Relapse by Logistic Regression

Some authors have stated that most infections in AECB are noninvasive and will eventually resolve spontaneously. However, because the relapse rate from AECB is high (11 to 32%), better strategies for treatment of an acute exacerbation are needed. Authors currently recommend treatment of AECB with antibiotics if the patient presents with moderate to severe symptoms, but these authors state that patients with mild symptoms at presentation can be treated supportively.

Our data suggest that patients with documented COPD (even with mild symptoms at presentation) benefit from antibiotic therapy. However, the choice of antibiotic is important because the antibiotics were not all equally effective in lowering the risk of relapse.

One possibility for the high relapse rates of patients treated with amoxicillin is related to the increasing emergence of pathogen resistance. There are a significant number of reports of antimicrobial resistance among respiratory isolates common in patients with AECB (including Haemophilus influenzae, M catarrhalis, and S pneumoniae). This trend of increasing resistance has been reported across the United States, Canada, and Europe. Our institution (at the time of the study) had rates of resistance to amoxicillin of 30% for H influenzae isolates, 34% for S pneumoniae, and 32% for M catarrhalis.

The other antibiotics prescribed during the study period had resistance rates < 10%, with the exception of erythromycin (12% resistance for S pneumoniae) and trimethoprim/sulfamethoxazole (18% resistance for S pneumoniae). The elevated rates of resistance to amoxicillin suggest one possible explanation for the higher relapse rate observed in our patients who were treated with this medication.

Table 1 — Variables Identified as Risk Factors for Relapse by Logistic Regression

Variables	Wald x2 p Value	Coefficient	SE	Odds Ratio (95% Confidence Interval)
Amoxicillin	0.0056	1.22	0.44	3.37(1.44-8.13)
Any other antibiotic except amoxicillin	0.0001	-1.26	0.32	0.28 (0.15-0.53)
Coronary artery disease*	0.0002	1.72	0.46	5.60 (2.33-14.17)
Active smoking	0.0002	1.47	0.40	4.45 (2.09-10.13)