From the Guidelines

Vancomycin is the best antibiotic for infectious colitis and gastroenteritis, particularly for severe cases.

Vancomycin is recommended as the first-line treatment for severe Clostridioides difficile infection (CDI) due to its superior pharmacokinetic properties and higher clinical cure rates compared to metronidazole 1.
Metronidazole may be considered for mild to moderate CDI, but its use is limited due to the risk of cumulative and potentially irreversible neurotoxicity with repeated or prolonged courses 1.
Fidaxomicin is a valid alternative to vancomycin for the treatment of CDI, especially in patients at higher risk for recurrence, such as the elderly or those receiving concomitant antibiotics 1.
The recommended dose of vancomycin is 125 mg four times daily for 10 days, while fidaxomicin is recommended at 200 mg twice daily for 10 days 1.
In cases where oral therapy is impossible, vancomycin may be administered as a retention enema or via a nasogastric tube 1.
Colectomy should be considered in patients with severe CDI who do not respond to medical therapy, particularly those with perforation of the colon, systemic inflammation, or deteriorating clinical condition 1.

From the Research

The treatment for infectious colitis and gastroenteritis depends on the severity of the disease and the causative agent 2, 3.
For uncomplicated disease, oral metronidazole or vancomycin is equally efficacious 2.
In cases of severe disease, the optimal therapy has not been established 2.
For acute infectious enteritis, initial management should focus on fluid and electrolyte repletion and symptomatic care, with empiric antibiotic therapy considered if there are clinical or epidemiologic features suggesting a treatable bacterial origin or a high-risk host 3.
A quinolone is generally the best initial choice for empiric antibiotic therapy in acute infectious enteritis 3.

The role of antibiotics in the treatment of ulcerative colitis is limited, but vancomycin may be beneficial in the management of treatment-refractory ulcerative colitis as an adjunct to biologic therapy 4.
In Crohn's disease, antibiotics such as metronidazole and azathioprine may be used to decrease the recurrence of postoperative disease in high-risk patients 5.
The combination of metronidazole and azathioprine appears to be a therapeutic option to decrease the recurrence of postoperative Crohn's disease in high-risk patients 5.
Different antibiotics, including ciprofloxacin, metronidazole, and rifaximin, have been evaluated in clinical trials for the treatment of inflammatory bowel disease, with modest effects in decreasing disease activity and achieving remission 6.

The use of antibiotics in inflammatory bowel disease is limited by potential side effects, including Clostridium difficile infection and increasing antibiotic resistance 5, 6.
Relapses can occur in up to 15% of cases of antibiotic-associated diarrhea, and cannot be accurately predicted or prevented 2.