The objective of this trial is to evaluate if intraoperative intraperitoneal administration of fosfomycin, metronidazole and recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) followed by oral antibiotic for three days is as effective as the current intravenous antibiotic treatment given during and three days after appendectomy for perforated appendicitis. The primary outcome is the total length of hospital stay, defined as the number of hours in hospital after end of operation and until 30-day follow-up.

Inclusion Criteria:

• Age ≥18 years
• Suspicion of acute appendicitis and planned for diagnostic laparoscopy and eventual laparoscopic appendectomy
• Perforated appendicitis (diagnosed during surgery by the surgeon)
• Negative p-HCG (women)
• Written informed consent after written and verbal information (preoperatively for the intervention group and postoperatively for the control group)

Exclusion Criteria:

• Cannot understand, read or speak Danish
• Previous allergic reaction to fosfomycin, metronidazole, rhGM-CSF, or penicillins e.g. piperacillin or amoxicillin
• Diagnostic laparoscopy revealing normal appendix not requiring an appendectomy or appendicitis without perforation
• Other intra-abdominal pathology requiring surgical intervention at the same operation
• Known renal or hepatic disease or biochemical evidence at the time of admission
• Known hematologic disease in current medical treatment
• American Society of Anesthesiologists (ASA) physical status ≥4 (a patient with severe systemic disease that is a constant threat to life)
• Body weight >110 kg
• Surgery converted to open appendectomy
• Anticipated compliance problems