Clinical Conundrums: Should You Give the First Dose of Antibiotics IV Before Discharging Home on Oral Antibiotics?

Bottom Line Up Top: In patients with infectious processes that are stable for discharge home, there is no role for giving a first dose of antibiotics IV in the ED.

Clinical Scenario: A 45-year-old woman with hypertension presents with a productive cough and fever. Her vitals are: HR 115, BP 120/80, Temp 102.8, O2 Sat 99% on RA, RR 18. A CXR demonstrates a right middle lobe opacity. After acetaminophen, her HR is 82 and her temp is 98.5. You decide she is stable to be discharged home on levofloxacin (See REBEL EM for antibiotic coverage in CAP) but consider giving her a first dose intravenously.

What Your Gut Says: Give the first dose IV! Jump start those antibiotics so the patient will get better faster.

What The Evidence Says: 

Many medical professionals believe that IV antibiotics are superior to oral antibiotics. This feels intuitive as the IV route seems like it would be stronger, faster, and fix the patient better than the oral route. Except for patients with poor gut absorption or those with critical infectious processes such as septic shock or necrotizing fasciitis, this belief appears to be unfounded. The majority of antibiotics we prescribe on a regular basis have excellent bioavailability through the oral route (see table below) (MacGregor 1997). For example, the bioavailability for oral levofloxacin, as used in our patient, is 99%. The infection doesn’t care how the antibiotic reached it, only that it did in fact get there.

Antibiotic Group Antibiotic Absorption (%)
Penicillins Amoxicillin 74-92
Amoxicillin/clavulanate (equivalent to ampicillin/sulbactam) 60
Ampicillin 30-55
Penicillin 60-73
Cephalosporins Cephalexin (equivalent to cefazolin) 90-100
Cefuroxime 30-52
Cefpodoxime (equivalent of ceftriaxone) 29-53
Macrolides Azithromycin 37
Clarithromycin 55
Tetracyclines Doxycycline > 90
Tetracycline > 90
Quinolones Ciprofloxacin 65-85
Levofloxacin 99
Moxifloxacin 90
Other Clindamycin 90
Metronidazole 80
TMP-SMX 70-90


While the effectiveness of antibiotics can be influenced by host factors or the dose given (i.e. a low bioavailability can be overcome by giving a larger dose), bioavailability is still a good place to start. Even better would be to see studies comparing one route to the other. We have a number of studies in adults and kids that do just that:

Study Format Comparison Findings Notes
Rae 2017 Observational Study IV vs oral clarithromycin No difference in mortality, ICU admission or time to clinical stability
Siegel 1996 Prospective, randomized, parallel group trial IV antibiotics (of different durations) followed by PO No difference in clinical course or cure rate 3 arms: 2 days IV + 8 days PO vs 5 days IV + 5 days PO vs 10 days IV
Oosterheert 2006 Open Label RCT IV antibiotics for full course vs partial course No difference in clinical course or hospital length of stay 3 days of IV + 4 days PO vs 7 days of IV
Castro-Guardiola 2001 Open Label RCT IV vs oral antibiotics No difference in mortality, clinical course or resolution Course was 7 days in non-severe and 10 days in severe pneumonia
Vogel 1991 Open Label RCT IV cefotaxime vs oral temafloxacin No difference in clinical cure rate
Addo-Yobo 2004 Open Label RCT IV penicillin vs oral amoxicillin No difference in treatment failure Pediatric CAP
Atkinson 2007 Open Label RCT IV penicillin vs oral amoxicillin No difference in time to clinical improvement Pediatric CAP
Rojas 2006 Meta-analysis IV vs oral antibiotics No difference in clinical improvement

While none of these studies is perfect, (we have no large, multicenter, randomized, controlled, double-blind studies) there isn’t a single study showing either superiority of IV antibiotics or inferiority of oral antibiotics. This finding persists when looking at a number of other infections including skin and soft tissue infections (SSTI) (First10EM), pyelonephritis (Strohmeier 2014) and even bone and joint infections (Li 2019). Additionally, multiple studies demonstrate increased harm with IV antibiotics such as increased rate of diarrhea (Haran 2014), complications from IV placement (Li 2015), and increased length of stay or cost (Lorgelly 2010).

Bottom Line: The weight of the evidence shows no benefit in treating a stable patient with CAP, SSTI or UTI with IV antibiotics or with a single dose of IV antibiotics followed by an oral antibiotic course. Furthermore, there are real harms associated with unnecessary IV antibiotics. The practice of a single dose of IV antibiotics prior to discharging home with a course of oral antibiotics should be ended.

Read More


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Post Peer Reviewed By: Salim R. Rezaie, MD (Twitter/X: @srrezaie)

Cite this article as: Anand Swaminathan, "Clinical Conundrums: Should You Give the First Dose of Antibiotics IV Before Discharging Home on Oral Antibiotics?", REBEL EM blog, January 9, 2024. Available at:

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