Aminopenicillins and Beta-lactamase Inhibitors

Mechanism

💊 Generic and Commercial Names

Amoxicillin + Clavulanic Acid (Augmentine, Clavumox), Ampicillin + Sulbactam (Unasyn), Piperacillin + Tazobactam (Tazocel).

🔬 Pharmacological Group

Extended-spectrum beta-lactams combined with suicidal beta-lactamase inhibitors.

Mechanism of Action

The combination associates a classic wall bactericidal agent with an enzyme inhibitor:

• Penetration by Porins: The charged lateral amino group of amoxicillin and ampicillin decreases their hydrophobicity, facilitating their passage through porin channels (such as OmpF and OmpC) in Gram-negative bacteria to access PBPs in the periplasmic space.
• Suicidal Enzyme Inhibition: Clavulanic acid, sulbactam and tazobactam are beta-lactams with little or no intrinsic antibacterial activity. They irreversibly bind to the serine residue of Class A beta-lactamases (including ESBL in the case of tazobactam) forming a stable acyl-enzyme complex that undergoes chemical rearrangements that permanently destroy the enzyme ("suicide inhibitors"). This protects the accompanying antibiotic from hydrolysis.
• Ureidopenicillins (Piperacillin): It has a lateral urea group that increases the binding affinity for PBP3 of Pseudomonas aeruginosa, facilitating its lytic action on this opportunistic pathogen.

Pharmacokinetics

Key Pharmacokinetics

Antimicrobial Spectrum

• Amoxicillin + Clavulanone / Ampicillin + Sulbactam: Excellent against Streptococcus spp., Enterococcus faecalis (susceptible to ampicillin), Staphylococcus aureus sensitive to methicillin, Haemophilus influenzae and Moraxella catarrhalisbeta-lactamase producers, sensitive enterobacteria and anaerobes such as Bacteroides fragilis.
• Piperacillin + Tazobactam: Very broad spectrum. Covers Gram-positives (except MRSA and VRE), anaerobes and critical Gram-negatives, including Pseudomonas aeruginosa, and non-carbapenemase-producing Enterobacteriaceae or MBL. It has variable coverage against strains with inducible AmpC.

Indicators and dose

Dosage and Adjustment

• Amoxicillin/Clavulanate (Oral): 875/125 mg every 8 hours or 1000/125 mg every 12 hours in healthy adults.
• Ampicillin/Sulbactam (IV): 1.5 g to 3.0 g every 6 hours via IV.
• Piperacillin/Tazobactam (IV): 4.5 g every 6 hours (or every 8 hours as an extended 4-hour infusion).
• Pip-Tazo Kidney Failure Adjustment:
  • Cl_cr 20-40 mL/min: Reduce dose to 3.375 g every 6 hours or 4.5 g every 8 hours.
  • Cl_cr < 20 mL/min: Reduce to 2.25 g every 6 hours or 3.375 g every 8 hours.

Security

Contraindications and ADRs

• Contraindications: Severe crossed allergy to beta-lactams. History of cholestatic jaundice or liver dysfunction associated with amoxicillin-clavulanate.
• Adverse Effects (ADR):
  • Gastrointestinal (Very common with Clavulanate): Profuse watery diarrhea (due to stimulation of intestinal motility mediated by clavulanate), nausea, vomiting, superinfection by Clostridioides difficile.
  • Hepatotoxicity: Acute cholestatic hepatitis or transaminasitis associated with clavulanate salt (more common in elderly patients or with treatments longer than 14 days).
  • Hematological: Reversible platelet dysfunction in high doses of piperacillin due to interference with ADP receptors on the platelet membrane.

Extended Piperacillin-Tazobactam Infusion Strategy

Being a beta-lactam with time-dependent PK/PD behavior, the efficacy of Piperacillin-Tazobactam is maximized when the concentrations of the free fraction exceed the MIC of the pathogen for as long as possible (%T > MIC). In critical patients with sepsis or septic shock (especially against Pseudomonas aeruginosa), the extended infusion is preferably prescribed (administer the dose of 4.5 g diluted in 100 mL of physiological solution to be administered over 4 hours every 8 hours, preceded by a rapid loading dose if it is the beginning of treatment). This doubles the optimal exposure time compared to the classic 30-minute infusion.