What’s the Critical Threshold in Time for Administering Antibiotics in CAP?

Abstract & Commentary

Source: Silber SH, et al. Early administration of antibiotics does not shorten time to clinical stability in patients with moderate to severe community-acquired pneumonia. Chest 2003;24:1798-1804.

The objective of this prospective observational study was to determine if there was a significant difference in time to clinical stability (TCS) between patients with moderate-to-severe community-acquired pneumonia (CAP) who received their antibiotics within four hours and those who received antibiotics after four hours. Study patients were adults admitted to the hospital from the emergency department (ED) with moderate-to-severe CAP as defined by a previously described classification system using a pneumonia severity index.1 TCS was defined as the first day that six parameters were met, including data about vital signs, oxygen saturation, and ability to eat.2 Patients who did not receive antibiotics consistent with standard guidelines were excluded.

Study groups were defined as those patients who received their first dose of antibiotics within four hours (group 1); within 4-8 hours (group 2); and more than eight hours (group 3) from triage. Of the 409 patients who achieved clinical stability during their hospital stay, the mean time to receiving antibiotics was 2.19 hours in group 1 (222 patients), 5.59 hours in group 2 (136 patients), and 13.07 hours in group 3 (51 patients). The mean TCS was 3.19 (SD 4.27) days in group 1, 3.16 (SD 4.48) days in group 2, and 3.29 (SD 4.31) days in group 3, with no statistically significant differences between the study groups. Secondary outcomes compared study groups for differences in mean length of stay, mean pneumonia severity index, and mortality — and no significant differences were found. The authors concluded that antibiotics administered within four hours do not reduce TCS in adult patients with moderate to severe CAP.

Commentary by Stephanie B. Abbuhl, MD, FACEP

These findings are not surprising, given that the study design was observational and there was no control of other factors that undoubtedly are important in determining TCS, such as length of illness before presentation to the ED, comorbid conditions, immunocompromise, nutritional status, use of oral antibiotics before presentation, and others.

These results are somewhat conflicting with those from other studies that have shown a correlation between outcome measures, such as reducing mortality and length of stay, and timeliness of antibiotics in CAP.3,4 In one study, antibiotics administered within eight hours were shown to reduce 30-day mortality in patients at least 65 years old. It is difficult to sort out just how critical the time to antibiotics is in CAP and what standard we should be held to. No one would dispute that sooner is better. However, picking a number of hours from triage-to-antibiotic to use as a quality indicator has significant implications and must be evidence-based and of proven benefit. The Center for Medicare and Medicaid Services now specifies a four-hour goal as a quality measure, revised from their previous target of eight hours. Given the conflicting data on this complex issue, and the fact that some of the studies that were the basis of the recommendation were significantly flawed, it seems that a four-hour standard for all patients should be critically reviewed. Further studies are needed to explore the possibility that only certain subgroups of patients may benefit from a more aggressive triage-to-antibiotic effort. Then we could justify focusing our limited resources on this goal while we divert our resources from other goals that may be equally as important. 

Dr. Abbuhl, Medical Director, Department of Emergency Medicine, The Hospital of the University of Pennsylvania; Associate Professor of Emergency Medicine, University of Pennsylvania School of Medicine, Philadelphia, is on the Editorial Board of Emergency Medicine Alert.


1. Fine MJ, et al. A prediction rule to identify low-risk patients with community-acquired pneumonia. N Engl J Med 1997;336:1730-1754.

2. Halm EA, et al. Time to clinical stability in patients hospitalized with community-acquired pneumonia. JAMA 1998;279:1452-1457.

3. Meehan TP, et al. Quality of care, process, and outcomes in elderly patients with pneumonia. JAMA 1997;23:2080-2084.

4. Battleman DS, et al. Rapid antibiotic delivery and appropriate antibiotic selection reduce length of stay of patients with community-acquired pneumonia. Arch Intern Med 2002;162:682-688.