Chemical Structure and Origin
Historically, the first monobactam was isolated during microbiological studies from cultures of the bacterium Chromobacterium violaceum. Unlike most other $\beta$-lactams (such as penicillins or cephalosporins), the monobactam molecule has a simplified structure containing only a single monocyclic $\beta$-lactam ring. This structural feature largely determines aztreonam's unique pharmacological profile and the absence of significant cross-allergenicity with other antibiotic classes.
Antimicrobial Spectrum and Selectivity Mechanism
Aztreonam exhibits marked selectivity, targeting exclusively Gram-negative microorganisms.
Its high-activity spectrum includes:
- Enteric pathogens: Salmonella and Shigella.
- Members of the Enterobacteriaceae family: Escherichia coli, Klebsiella species, and Proteus species.
- Problematic hospital-acquired pathogens, most notably Pseudomonas aeruginosa.
- Respiratory and central nervous system pathogens: Haemophilus influenzae and Neisseria meningitidis.
- The causative agent of gonorrhea: Neisseria gonorrhoeae.
At the same time, the drug is completely devoid of activity against Gram-positive bacteria and all anaerobes (including Bacteroides species).
This strict selectivity is explained by how it interacts with bacterial enzymes. Aztreonam demonstrates high stability against many $\beta$-lactamases produced by Gram-negative bacteria. However, enzymes produced by Gram-positive microorganisms and anaerobes readily hydrolyze the monocyclic ring of the antibiotic, rendering it ineffective against these pathogens.
Clinical Pharmacology and Indications
In clinical practice, aztreonam holds the status of a reserve drug. A key indication for selecting this antibiotic is the need to treat severe infections in patients with documented, severe penicillin allergies (owing to low cross-allergenicity).
It is used for a wide range of pathologies, as well as in cases where other antibiotics fail:
- Lower respiratory tract infections (including nosocomial pneumonia).
- Intra-abdominal infections and pelvic inflammatory disease.
- Severe urinary tract infections.
- Purulent-inflammatory processes of the skin, soft tissues, bone, and joints.
- Generalized life-threatening conditions: sepsis and bacterial meningitis.
Dosage Regimen and Adverse Reactions
Aztreonam is administered exclusively parenterally via intravenous (IV) or intramuscular (IM) injections. The dosing frequency is every 8 to 12 hours.
- Gastrointestinal: various dyspeptic symptoms.
- Allergic manifestations: skin reactions.
- Central nervous system: headache.
- Local reactions: phlebitis at the intravenous injection site.