Intra-abdominal infection

Red Flags

Sepsis or septic shock with intra-abdominal source — sepsis pathway with broad-spectrum IV antibiotic within 1 h, fluids, lactate, blood cultures, urgent source control^[1]
Generalised peritonitis with peritonism on examination — emergency surgery; do not delay for imaging if hemodynamically stable enough^[1]
Fecal peritonitis or anastomotic leak — emergency damage-control surgery; ITU; broader cover^[1]
Failure of source control at 48–72 h with persistent sepsis — repeat imaging and reoperation; consider ESBL or fungal coverage^[1]

First-line treatment

Interventions

Source control as cornerstone^[1]
Surgical or radiologic drainage of pus collections, repair or resection of perforation, exteriorisation; achieve within 24 h of diagnosis when feasible; antibiotics alone are inadequate
Resuscitation and supportive care^[1]
Sepsis bundle: fluid 30 mL/kg crystalloid, vasopressors for MAP <65 after fluid, lactate-guided; oxygen, glycaemic control; nutrition early when feasible
Risk-stratified antibiotic choice^[1]
Community-acquired non-severe: narrower spectrum (cefazolin + metronidazole or co-amoxiclav). Severe community-acquired or healthcare-associated: piperacillin-tazobactam or meropenem; add MRSA cover if risk; antifungal if recurrent or upper-GI perforation
Antibiotic duration^[1]
After adequate source control: 4 days (STOP-IT trial) for adequately drained collections; longer for inadequate source control or persistent sepsis; switch IV to oral when clinically improving and oral tolerated

First-line drug therapy

Drug	Class	Adult	Paediatric	Notes
Piperacillin-tazobactam^[1]	Beta-lactam + beta-lactamase inhibitor	4.5 g IV every 6–8 h (extended infusion 4 h preferred where available)	Per local protocol	First-line for severe community-acquired and healthcare-associated; broad gram-positive, gram-negative, anaerobic; renal dose adjustment
Meropenem^[1]	Carbapenem	1 g IV every 8 h (extended infusion or 2 g if MIC concern)	20 mg/kg every 8 h	Severe healthcare-associated, ESBL coverage, prior multi-resistant organism; renal dose adjustment; reserve to limit resistance
Ceftriaxone + metronidazole^[1]	Third-generation cephalosporin + nitroimidazole	Ceftriaxone 1–2 g IV daily + metronidazole 500 mg IV every 8 h	Ceftriaxone 50–80 mg/kg/day; metronidazole 7.5 mg/kg every 8 h	Mild-moderate community-acquired; oral switch to cefuroxime + metronidazole when improving
Vancomycin or daptomycin (MRSA cover)^[1]	Glycopeptide / lipopeptide	Vancomycin 25–30 mg/kg loading then 15–20 mg/kg every 8–12 h with TDM target trough 15–20	60 mg/kg/day every 6 h	Add when MRSA risk (prior colonisation, healthcare-associated, persistent sepsis); narrow once cultures available
Echinocandin (caspofungin, micafungin) for fungal cover^[1]	Echinocandin antifungal	Caspofungin 70 mg IV loading then 50 mg daily; micafungin 100 mg daily	Caspofungin 70 mg/m² loading then 50 mg/m²; micafungin 2 mg/kg	Add for repeated upper-GI perforation, recurrent leakage, recent broad-spectrum antibiotic with persistent sepsis, or proven Candida intra-abdominal infection

Piperacillin-tazobactam^[1]

Beta-lactam + beta-lactamase inhibitor

Adult: 4.5 g IV every 6–8 h (extended infusion 4 h preferred where available)
Paediatric: Per local protocol

First-line for severe community-acquired and healthcare-associated; broad gram-positive, gram-negative, anaerobic; renal dose adjustment

Meropenem^[1]

Carbapenem

Adult: 1 g IV every 8 h (extended infusion or 2 g if MIC concern)
Paediatric: 20 mg/kg every 8 h

Severe healthcare-associated, ESBL coverage, prior multi-resistant organism; renal dose adjustment; reserve to limit resistance

Ceftriaxone + metronidazole^[1]

Third-generation cephalosporin + nitroimidazole

Adult: Ceftriaxone 1–2 g IV daily + metronidazole 500 mg IV every 8 h
Paediatric: Ceftriaxone 50–80 mg/kg/day; metronidazole 7.5 mg/kg every 8 h

Mild-moderate community-acquired; oral switch to cefuroxime + metronidazole when improving

Vancomycin or daptomycin (MRSA cover)^[1]

Glycopeptide / lipopeptide

Adult: Vancomycin 25–30 mg/kg loading then 15–20 mg/kg every 8–12 h with TDM target trough 15–20
Paediatric: 60 mg/kg/day every 6 h

Add when MRSA risk (prior colonisation, healthcare-associated, persistent sepsis); narrow once cultures available

Echinocandin (caspofungin, micafungin) for fungal cover^[1]

Echinocandin antifungal

Adult: Caspofungin 70 mg IV loading then 50 mg daily; micafungin 100 mg daily
Paediatric: Caspofungin 70 mg/m² loading then 50 mg/m²; micafungin 2 mg/kg

Add for repeated upper-GI perforation, recurrent leakage, recent broad-spectrum antibiotic with persistent sepsis, or proven Candida intra-abdominal infection

Safety-net

Most intra-abdominal infections need surgical or radiologic drainage in addition to antibiotics — antibiotics alone are insufficient^[1]
Persistent fever, rising inflammatory markers, or hemodynamic instability after 48–72 h on appropriate antibiotic — investigate for inadequate source control or resistant organism^[1]
Take antibiotics for the full prescribed course; review at 4 days for switch to oral and discontinuation in adequately drained collections^[1]

Referral criteria

Suspected complicated intra-abdominal infection or peritonitisEmergency department / general surgery^[1]
Septic shock or organ dysfunctionITU and surgical admission^[1]
Recurrent or refractory disease, anastomotic leak, intra-abdominal abscess on imagingTertiary surgery and interventional radiology^[1]
Resistant organism (ESBL, CRE, MDR Pseudomonas) on cultureInfectious diseases / antimicrobial stewardship^[1]

Clinical summary

Diagnosis, source control, and antibiotic management of complicated intra-abdominal infection in adults including community- and hospital-acquired peritonitis.

References

1.WSES Guidelines for Management of Intra-Abdominal Infections (2017, with 2024 update); IDSA / SIS Guideline on Complicated Intra-Abdominal Infection (2024)