What is the stability of Zavicefta (ceftazidime/avibactam) and aztreonam after reconstitution?

Stability of Zavicefta/Aztreonam After Reconstitution

For aztreonam, use reconstituted solutions within 48 hours at room temperature (15°C-30°C) or within 7 days if refrigerated (2°C-8°C) at concentrations ≤2% w/v; for Zavicefta (ceftazidime-avibactam), the stability is significantly more limited and problematic for extended storage, particularly in elastomeric devices used for outpatient therapy.

Aztreonam Stability (FDA-Approved)

The FDA labeling provides clear, authoritative guidance for aztreonam stability 1:

Standard Concentrations (≤2% w/v):

• Room temperature (15°C-30°C): 48 hours
• Refrigerated (2°C-8°C): 7 days

Higher Concentrations (>2% w/v):

• Use promptly after preparation for most diluents
• Exception: Solutions prepared with Sterile Water for Injection or 0.9% Sodium Chloride maintain the same 48-hour/7-day stability as lower concentrations 1

Admixtures with Other Antibiotics:

When aztreonam is mixed with other agents in 0.9% sodium chloride or 5% dextrose 1:

• With clindamycin, gentamicin, tobramycin, or cefazolin: Stable 48 hours at room temperature or 7 days refrigerated
• With ampicillin in 0.9% sodium chloride: 24 hours at room temperature, 48 hours refrigerated
• With ampicillin in 5% dextrose: Only 2 hours at room temperature, 8 hours refrigerated
• Incompatible with: Nafcillin, cephradine, and metronidazole

Ceftazidime-Avibactam (Zavicefta) Stability

The stability picture for ceftazidime-avibactam is considerably more complex and restrictive:

Critical Limitation - Pyridine Formation:

The major stability concern is pyridine accumulation, a degradation product that exceeds European Pharmacopeia limits even during refrigerated storage 2. This is a critical safety issue that limits practical use in extended infusion devices.

Elastomeric Device Studies:

Recent high-quality research reveals significant stability challenges 3, 2:

• After 14 days refrigerated storage (2°C-8°C) followed by 24 hours at 32°C:

  • Ceftazidime remaining: 75.5%-85.4% (depending on concentration and device)
  • Avibactam remaining: 83.2%-93.1%
  • Pyridine levels: Exceeded acceptable limits after refrigerated storage alone 2

• For OPAT use: Degradation remains <10% for at least 12 hours of running phase only if stored refrigerated for ≤72 hours prior to use 3

Practical Recommendation for Combined Therapy:

When using ceftazidime-avibactam with aztreonam (for metallo-β-lactamase producers):

• Y-site compatibility is confirmed at clinically relevant concentrations 4:

  • Ceftazidime-avibactam: 8,25, and 50 mg/mL
  • Aztreonam: 10 and 20 mg/mL
  • Compatible for at least 12 hours after mixing

• Administer as simultaneous infusions rather than pre-mixed solutions to avoid extended storage stability issues 5

Clinical Algorithm for Storage and Use

For Aztreonam Alone:

1. Reconstitute to ≤2% w/v concentration
2. Store refrigerated (2°C-8°C) for up to 7 days OR
3. Keep at room temperature for up to 48 hours
4. Inspect for color changes (slight pink tint acceptable) or particulates before use 1

For Ceftazidime-Avibactam:

1. Prepare fresh whenever possible
2. If advance preparation needed: refrigerate for maximum 72 hours before use 3
3. Do not use elastomeric devices for >12-hour infusions due to pyridine accumulation 2
4. Administer within 12 hours of reaching room/body temperature

For Combined Ceftazidime-Avibactam + Aztreonam:

1. Prepare each agent separately
2. Administer via Y-site simultaneously 4
3. Complete infusion within 12 hours of mixing
4. Use continuous or extended infusions (q6h preferred over q8h for optimal PK/PD) 5

Critical Pitfalls to Avoid

• Do not assume ceftazidime-avibactam has the same stability as aztreonam - it degrades much faster and produces toxic pyridine 2
• Do not pre-mix ceftazidime-avibactam and aztreonam for extended storage - administer simultaneously via Y-site instead 4
• Do not use 14-day refrigerated storage protocols developed for other antibiotics with ceftazidime-avibactam 3, 2
• Do not use ceftazidime-avibactam in 24-hour elastomeric pumps - pyridine limits are exceeded 2

The older guideline data showing ceftazidime stability of 21 days refrigerated 6 predates avibactam combination products and should not be extrapolated to Zavicefta.