FDA Approves Metronidazole Injection for Anaerobic Infections and Prophylaxis

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FDA Published April 29, 2026 Medically reviewed April 29, 2026 DOI ↗ By Dr. Amelia Tan, PhD · Internal Medicine & Chronic Disease

Key Takeaway

Consider metronidazole for serious anaerobic infections and prophylaxis in colorectal surgery; use only when bacterial infection is proven or strongly suspected.

The FDA has approved Metronidazole Injection USP for the treatment of serious infections caused by susceptible anaerobic bacteria, including intra-abdominal infections, skin and skin structure infections, gynecologic infections, bacterial septicemia, bone and joint infections, central nervous system infections, lower respiratory tract infections, and endocarditis. The drug is also indicated for prophylaxis to reduce postoperative infection in adult patients undergoing elective colorectal surgery classified as contaminated or potentially contaminated. This approval provides clinicians with an option for anaerobic infections, particularly those resistant to clindamycin, chloramphenicol, and penicillin. The label emphasizes using the drug only for proven or strongly suspected bacterial infections to reduce the development of drug-resistant bacteria.

＋ Clinical Details (Mechanism · Dosing · Trial Data · Warnings)

Mechanism of Action

Not reported in label.

Indication & Patient Population

Metronidazole Injection is indicated for treatment of serious anaerobic infections caused by susceptible bacteria, including: intra-abdominal infections (peritonitis, abscess), skin and skin structure infections, gynecologic infections (endometritis, tubo-ovarian abscess, post-surgical vaginal cuff infection), bacterial septicemia, bone and joint infections (adjunctive), CNS infections (meningitis, brain abscess), lower respiratory tract infections (pneumonia, empyema, lung abscess), and endocarditis. It is also indicated for prophylaxis in adult patients undergoing elective colorectal surgery classified as contaminated or potentially contaminated. For intra-abdominal infections, pediatric patients less than 4 months of age are included.

Dosing & Administration

Adults: Loading dose 15 mg/kg infused over one hour, then maintenance dose 7.5 mg/kg infused over one hour every 6 hours. First maintenance dose 6 hours after loading. Maximum 4 g in 24 hours. Usual duration 7-10 days; longer for bone/joint, lower respiratory, endocardium. Pediatric patients <4 months: dosing based on post-menstrual age (see Table 2 in label). Prophylaxis: administer preoperatively, intraoperatively, and postoperatively; discontinue within 12 hours after surgery.

Key Clinical Trial Data

Trial data not available in label.

Warnings & Contraindications

Not reported in label.

Place in Therapy

Metronidazole Injection is indicated for serious anaerobic infections, including those resistant to clindamycin, chloramphenicol, and penicillin. It should be used only for proven or strongly suspected bacterial infections to reduce resistance. In mixed infections, add appropriate aerobic coverage. Prophylactic use is limited to elective colorectal surgery.

Study Details

Study typeFda approval

PublishedSep 1983

View Original Abstract ↓

INDICATIONS AND USAGE To reduce the development of drug-resistant bacteria and maintain the effectiveness of Metronidazole Injection USP and other antibacterial drugs, Metronidazole Injection USP should be used only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria. When culture and susceptibility information are available, they should be considered in selecting or modifying antibacterial therapy. In the absence of such data, local epidemiology and susceptibility patterns may contribute to the empiric selection of therapy. TREATMENT OF ANAEROBIC INFECTIONS Metronidazole Injection is indicated in the treatment of serious infections caused by susceptible anaerobic bacteria. Indicated surgical procedures should be performed in conjunction with Metronidazole Injection therapy. In a mixed aerobic and anaerobic infection, antibacterial drugs appropriate for the treatment of the aerobic infection should be used in addition to Metronidazole Injection. Metronidazole Injection USP is effective in Bacteroides fragilis infections resistant to clindamycin, chloramphenicol, and penicillin. Intra-Abdominal Infections , including peritonitis, intra-abdominal abscess, and liver abscess, caused by Bacteroides species including the B. fragilis group ( B. fragilis, B. distasonis, B. ovatus, B. thetaiotaomicron, B. vulgatus), Clostridium species, Eubacterium species, Peptococcus species, and Peptostreptococcus species in adults and pediatric patients less than 4 months of age. Skin and Skin Structure Infections caused by Bacteroides species including the B. fragilis group, Clostridium species, Peptococcus species, Peptostreptococcus species, and Fusobacterium species in adults. Gynecologic Infections , including endometritis, endomyometritis, tubo-ovarian abscess, and post-surgical vaginal cuff infection, caused by Bacteroides species including the B. fragilis group, Clostridium species, Peptococcus species, and Peptostreptococcus species in adults. Bacterial Septicemia caused by Bacteroides species including the B. fragilis group and Clostridium species in adults. Bone and Joint Infections , as adjunctive therapy, caused by Bacteroides species including the B. fragilis group in adults. Central Nervous System (CNS) Infections , including meningitis and brain abscess, caused by Bacteroides species including the B. fragilis group in adults. Lower Respiratory Tract Infections , including pneumonia, empyema, and lung abscess, caused by Bacteroides species including the B. fragilis group in adults. Endocarditis caused by Bacteroides species including the B. fragilis group in adults. PROPHYLAXIS INDICATION The prophylactic administration of Metronidazole Injection preoperatively, intraoperatively, and postoperatively may reduce the incidence of postoperative infection in adult patients undergoing elective colorectal surgery which is classified as contaminated or potentially contaminated. Prophylactic use of Metronidazole Injection should be discontinued within 12 hours after surgery. If there are signs of infection, specimens for cultures should be obtained for the identification of the causative organism(s) so that appropriate therapy may be given (see DOSAGE AND ADMINISTRATION ). Usage To reduce the development of drug-resistant bacteria and maintain the effectiveness of metronidazole and other antibacterial drugs, metronidazole should be used only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria. When culture and susceptibility information are available, they should be considered in selecting or modifying antimicrobial therapy. In the absence of such data, local epidemiology and susceptibility patterns may contribute to the empiric selection of therapy.