What is the recommended antibiotic treatment for infections caused by gram-negative bacteria or unknown organisms?

From the Guidelines

For infections caused by gram-negative bacteria or unknown organisms, ampicillin is not the recommended first-line treatment, and penicillin is not effective against gram-negative bacteria, therefore, other antibiotics such as ciprofloxacin or ceftriaxone should be used as first-line treatment. When considering the treatment of infections caused by gram-negative bacteria or unknown organisms, it is crucial to select an antibiotic that is effective against a broad spectrum of pathogens.

• The British Thoracic Society guideline for bronchiectasis in adults 1 provides recommendations for antimicrobial agents based on the causative organism.
• For coliforms, such as Klebsiella and Enterobacter, oral ciprofloxacin 500 mg or 750 mg twice daily is recommended as first-line treatment, with intravenous ceftriaxone 2G once daily as an alternative 1.
• In cases of Pseudomonas aeruginosa infection, oral ciprofloxacin 500 mg twice daily (or 750 mg twice daily for more severe infections) is recommended, with intravenous ceftazidime 2G three times daily as an alternative 1.
• The choice of antibiotic should be guided by the severity of the infection, the susceptibility of the causative organism, and the patient's clinical response to treatment.
• It is essential to note that ampicillin and penicillin are not effective against many gram-negative bacteria, and their use may lead to treatment failure and the development of antibiotic resistance.
• Therefore, ciprofloxacin or ceftriaxone should be used as first-line treatment for infections caused by gram-negative bacteria or unknown organisms, with adjustments made based on culture and sensitivity results 1.

From the FDA Drug Label

To reduce the development of drug-resistant bacteria and maintain the effectiveness of Ampicillin capsules, Ampicillin for Oral Suspension and other antibacterial drugs, Ampicillin capsules and Ampicillin for Oral Suspension should be used only to treat or prevent infections that are proven or strongly suspected to be caused by bacteria Ampicillin capsules and Ampicillin for oral suspension are indicated in the treatment of infections caused by susceptible strains of the designated organisms listed below: Infections of the genitourinary tract including gonorrhea - E. coli, P. mirabilis, enterococci, Shigella, S. typhosa and other Salmonella and nonpenicillinase-producing N. gonorrhoeae Infections of the respiratory tract - Nonpenicillinase-producing H. influenzae and staphylococci, and streptococci including Streptococcus pneumoniae.

The recommended antibiotic treatment for infections caused by gram-negative bacteria or unknown organisms is Ampicillin.

• Key points:
  • Ampicillin is effective against gram-negative bacteria such as E. coli, P. mirabilis, and Salmonella.
  • It is also effective against infections of the respiratory tract caused by nonpenicillinase-producing H. influenzae and streptococci.
  • The choice of antibiotic should be based on culture and susceptibility information, or local epidemiology and susceptibility patterns if such data is not available 2

From the Research

Comparison of Ampicillin and Penicillin

• Ampicillin is a beta-lactam antibiotic with a broader spectrum of activity than penicillin, including effectiveness against Gram-negative bacteria 3.
• Penicillin is not mentioned in the provided studies as a comparison to ampicillin, but ampicillin is compared to other antibiotics such as ceftriaxone 4, 5.
• Ampicillin/sulbactam is a combination antibiotic with activity against Gram-positive, Gram-negative, and anaerobic bacteria, and has been shown to be effective in various severe bacterial infections 3.

Antibiotic Treatment for Infections Caused by Gram-Negative Bacteria or Unknown Organisms

• Ceftriaxone is a third-generation cephalosporin with a broad spectrum of activity against Gram-positive and Gram-negative bacteria, and has been shown to be effective in treating various infections, including those caused by multidrug-resistant Gram-negative bacteria 6.
• Ampicillin/sulbactam has been shown to be effective in treating infections caused by Gram-negative bacteria, including Acinetobacter baumannii 3.
• The use of ampicillin/sulbactam has been associated with a lower incidence of colonization by Acinetobacter spp. and improved susceptibility of Pseudomonas aeruginosa to ciprofloxacin 7.
• A study comparing ceftriaxone and ampicillin for the treatment of community-acquired pneumonia found that ampicillin was associated with comparable clinical outcomes and a lower rate of Clostridioides difficile infection 5.

Key Findings

• Ampicillin/sulbactam is a effective antibiotic combination for treating various severe bacterial infections, including those caused by Gram-negative bacteria 3.
• Ceftriaxone is a effective antibiotic for treating infections caused by Gram-negative bacteria, including multidrug-resistant strains 6.
• The use of ampicillin/sulbactam may be associated with a lower incidence of colonization by resistant bacteria and improved susceptibility of Pseudomonas aeruginosa to ciprofloxacin 7.
• Ampicillin may be a suitable alternative to ceftriaxone for the treatment of community-acquired pneumonia, with comparable clinical outcomes and a lower rate of Clostridioides difficile infection 5.