From the Guidelines

Complicated diverticulitis requires antibiotic treatment.

The choice of antibiotics should cover both gram-negative and anaerobic bacteria.
Broad-spectrum antibiotics such as a combination of an oral fluoroquinolone and metronidazole or monotherapy with oral amoxicillin-clavulanate are commonly used in the outpatient setting for mild uncomplicated diverticulitis 1.
In the inpatient setting, various antibiotic regimens are used, but the evidence is insufficient to determine the comparative effectiveness of different regimens 1.
The duration of antibiotic treatment is usually 4-7 days, but can be longer based on the patient's general health status, immune status, severity of presentation, CT findings, and patient expectations 1.

Immunocompromised patients should be treated with antibiotics due to their high risk of complications 1.
Patients with complicated diverticulitis or uncomplicated diverticulitis with a fluid collection or longer segment of inflammation on CT scan should also be treated with antibiotics 1.
Patients with comorbidities or frailty, refractory symptoms or vomiting, or elevated CRP or white blood cell count should be considered for antibiotic treatment 1.

The evidence for the use of antibiotics in complicated diverticulitis is based on low-certainty evidence, but the potential benefits of treatment outweigh the harms 1.
The choice of antibiotics and duration of treatment should be individualized based on patient-specific factors and clinical judgment 1.

From the Research

The use of broad-spectrum and appropriate antibiotics is recommended for patients with complicated acute diverticulitis, especially those with comorbidities, sepsis, or immunodeficiency 2.
For complicated diverticulitis, antibiotics should be used in combination with other treatments such as modified diet or bowel rest, and pain control 3.
The selection of specific antimicrobial agents for the treatment of acute diverticulitis is based on the general recommendation to use antibiotics with activity against common gram-negative and anaerobic pathogens 4.
Episodes of diverticulitis severe enough to warrant hospitalization should be managed initially with intravenous antibiotics, while oral therapy can be used for outpatient treatment or when the patient's condition improves 4.

Treatment decisions for diverticulitis are based on the categorization of disease as complicated vs. uncomplicated 3.
Complicated acute diverticulitis may require interventional radiology or surgery, although the best surgical approach remains a matter of discussion 2.
Patients with uncomplicated diverticulitis may be treated without antibiotics, but this decision should be made on a case-by-case basis, taking into account the patient's overall health and risk factors 5, 6.

There is little evidence to base the selection of specific antimicrobial regimens for the treatment of acute diverticulitis, and no regimen has demonstrated superiority 4.
A number of single agents and combination regimens provide activity against common gram-negative and anaerobic pathogens, but careful clinical studies are needed to evaluate better the antibiotic regimens for the treatment of acute diverticulitis 4.