What is the effectiveness and dosing of Unasyn (ampicillin-sulbactam) for anaerobic infections?

From the Guidelines

Ampicillin-sulbactam (Unasyn) is effective for many anaerobic infections, typically dosed at 1.5-3g IV every 6 hours for adults (1g ampicillin plus 0.5g sulbactam to 2g ampicillin plus 1g sulbactam) 1.

Key Points

• For severe infections, the higher dose is recommended.
• Treatment duration generally ranges from 7-14 days depending on infection severity and clinical response.
• Dosage adjustments are necessary for patients with renal impairment: for creatinine clearance 15-29 mL/min, administer every 12 hours; for <15 mL/min, administer every 24 hours.
• Ampicillin-sulbactam works well against many anaerobes including Bacteroides fragilis, Prevotella, Fusobacterium, and Peptostreptococcus species, making it suitable for intra-abdominal infections, diabetic foot infections, aspiration pneumonia, and gynecological infections.

Mechanism and Precautions

• The effectiveness stems from sulbactam's beta-lactamase inhibition, which protects ampicillin from enzymatic degradation by anaerobic bacteria.
• Monitor patients for allergic reactions, especially those with penicillin allergies, and be aware that prolonged use may lead to superinfections with resistant organisms.
• Clinical improvement should be evident within 48-72 hours of initiating therapy.

Specific Considerations

• According to the guidelines for the diagnosis and management of skin and soft tissue infections, ampicillin-sulbactam is recommended for infections following animal or human bites, with a dosage of 1.5–3.0 g every 6–8 hours 1.
• The choice of antibiotic should be based on the suspected or confirmed pathogens, as well as the patient's medical history and allergy profile.
• It is essential to note that ampicillin-sulbactam may not be effective against all anaerobic organisms, and alternative treatments may be necessary in certain cases.

From the FDA Drug Label

Ampicillin and sulbactam for injection is indicated for the treatment of infections due to susceptible strains of the designated microorganisms in the conditions listed below. Intra-Abdominal Infections caused by beta-lactamase producing strains of Escherichia coli, Klebsiella spp. (including K. pneumoniae*), Bacteroides spp. (including B. fragilis), and Enterobacter spp. Gynecological Infections caused by beta-lactamase producing strains of Escherichia coli,* and Bacteroides spp. * (including B. fragilis*). Skin and Skin Structure Infections caused by beta-lactamase producing strains of Staphylococcus aureus, Escherichia coli,* Klebsiella spp. * (including K. pneumoniae*), Proteus mirabilis,* Bacteroides fragilis,* Enterobacter spp.,* and Acinetobacter calcoaceticus.

The effectiveness of Unasyn (ampicillin-sulbactam) for anaerobic infections is supported by its indication for the treatment of:

• Intra-abdominal infections caused by beta-lactamase producing strains of Bacteroides spp. (including B. fragilis)
• Gynecological infections caused by beta-lactamase producing strains of Bacteroides spp. (including B. fragilis)
• Skin and skin structure infections caused by beta-lactamase producing strains of Bacteroides fragilis The recommended adult dosage of ampicillin and sulbactam for injection is 1.5 grams to 3 grams every six hours 2. The total dose of sulbactam should not exceed 4 grams per day. For pediatric patients, the recommended daily dose is 300 mg per kg of body weight administered via intravenous infusion in equally divided doses every 6 hours 2.

From the Research

Unasyn Anaerobic Coverage

• Unasyn, a combination of ampicillin and sulbactam, has been shown to be effective against anaerobic infections 3, 4.
• The combination of ampicillin and sulbactam has been found to be more effective than ampicillin alone against Bacteroides fragilis strains, a common cause of anaerobic infections 4.
• Unasyn has a broad spectrum of activity against Gram-positive and Gram-negative aerobic and anaerobic bacteria, making it a valuable agent in the treatment of various infections 5.

Effectiveness Against Specific Anaerobic Bacteria

• Unasyn has been shown to be effective against Bacteroides fragilis group isolates, with 98-99% of strains inhibited at breakpoint concentrations 4.
• The combination of ampicillin and sulbactam is also effective against other anaerobic bacteria, including Fusobacterium spp., gram-positive rods, and gram-positive cocci 4.
• However, resistance to Unasyn has been reported in some anaerobic bacteria, including certain members of the Bacteroides fragilis group 3, 6.

Dosing and Administration

• Unasyn is typically administered intravenously, with peak serum levels reached within 15 minutes to 1 hour after infusion 7.
• The dosing of Unasyn may vary depending on the specific infection being treated and the patient's renal function 5.
• Unasyn is available in both parenteral and oral forms, with the oral form (sultamicillin) being effective in the treatment of mild to moderate infections 5.