Aztreonam (Azactam) is an antibiotic belonging to a class known as monocyclic beta-lactam antibiotics (Monobactams). Aztreonam is not affected by beta-lactamases, therefore, it is used in the treatment of gram-negative infections, especially of the meninges, bladder, and kidneys.
It is a manufactured version of a chemical from the bacterium Chromobacterium violaceum.
Class
- Monobactam (Monocyclic β-lactam antibiotic)
Mechanism of Action
- Inhibits bacterial cell wall synthesis by binding to penicillin-binding protein 3 (PBP-3) .
- Prevents cross-linking of peptidoglycan → bactericidal against susceptible aerobic Gram-negative bacteria .
- No significant activity against Gram-positive organisms or anaerobes.
Spectrum of Activity
Effective against:
- Pseudomonas aeruginosa
- Escherichia coli
- Klebsiella spp.
- Haemophilus spp.
- Proteus spp.
- Serratia spp.
- Enterobacter spp.
- Citrobacter spp.
Ineffective or resistant organisms:
- Gram-positive cocci (e.g., Staphylococcus aureus , Streptococcus spp. )
- Anaerobes (e.g., Bacteroides )
- Xanthomonas maltophilia
- Aeromonas hydrophila
- Streptococcus pyogenes
Clinical Indications
- Moderate to severe infections caused by aerobic Gram-negative bacteria:
- Urinary tract infections (UTIs)
- Pneumonia (including ventilator-associated)
- Sepsis
- Intra-abdominal infections
- Endometritis
- Bone infections (e.g., osteomyelitis)
- Pelvic inflammatory disease
- Febrile neutropenia
- Skin and soft tissue infections
- Peritonitis
- Inhaled aztreonam (Cayston®) :
- FDA-approved for cystic fibrosis-related pulmonary infections
- Off-label : Non-CF bronchiectasis, COPD exacerbations, post-lung transplant infections
Dosage & Administration
Route
- Parenteral (IV/IM) or Inhalation (Nebulized)
Adult Dosage
- Moderate infections : 1–2 g IV/IM q8–12h
- Severe infections : 2 g IV q6–8h (Max: 8 g/day)
- Cystic fibrosis (inhaled) : 75 mg nebulized TID for 28 days on/off cycles
- Duration: Varies (7–21 days depending on infection severity)
Pediatric Dosage
- IV: 30 mg/kg q6–8h (max 2 g/dose or 8 g/day)
- Inhaled (≥7 years): Same as adult dose for CF
Renal Adjustments
- CrCl 10–30 mL/min : 1–2 g loading dose, then 50% of usual dose
- Hemodialysis : Administer post-dialysis
Pharmacokinetics
- Poor oral absorption → must be given IV/IM or inhaled
- Crosses the blood-brain barrier (useful for meningitis)
- Excreted unchanged in urine → renal dosing required
Side Effects
Common
- Local: Pain, erythema at injection site
- GI: Diarrhea, nausea, vomiting
- Skin: Rash
Rare but Serious
- Clostridioides difficile-associated diarrhea (CDAD)
- Toxic epidermal necrolysis
- Drug-induced eosinophilia
- Anaphylaxis (esp. if ceftazidime-allergic)
Allergy and Cross-Reactivity
- Safe in most penicillin/cephalosporin allergies
- Exception : Cross-reactivity with ceftazidime due to similar side chain
- Use with caution in ceftazidime-allergic patients
Drug Interactions
- Synergistic with aminoglycosides (e.g., tobramycin , arbekacin ) against P. aeruginosa
- Compatible with β-lactam antibiotics in combination therapy
Pregnancy Category
- Category B : No known teratogenic effects; generally considered safe in pregnancy
High-Yield Notes
- Aztreonam is β-lactamase-resistant , but not effective against ESBL-producing bacteria
- Ideal for patients with severe β-lactam allergy (except ceftazidime)
- Does not cover Gram-positives or anaerobes → not suitable as monotherapy for mixed infections
- Inhaled form (Cayston®) significantly improves lung function in CF
Memory Aids
- A ztreonam = A erobic Gram-negative coverage only
- Think “Aztreonam = Alone vs. Aerobes”
- Avoid in ceftazidime allergy
