Chemical structure and origin
Historically, the first representative of monobactams was isolated during microbiological studies from a culture of the bacterium Chromobacterium violaceum. Unlike most other $\beta$-lactams (e.g., penicillins or cephalosporins), the monobactam molecule has a simplified structure—it contains only a single monocyclic $\beta$-lactam ring. This structural feature largely determines aztreonam's unique pharmacological profile and the absence of pronounced cross-allergy with other classes of antibiotics.
Antimicrobial spectrum and mechanism of selectivity
Aztreonam exhibits pronounced selectivity. Its target is exclusively gram-negative microorganisms.
The spectrum of high activity of the drug includes:
- Pathogens of intestinal infections: Salmonella (Salmonella) and Shigella (Shigella).
- Members of the Enterobacteriaceae family: Escherichia coli (Escherichia coli), Klebsiella (Klebsiella), Proteus (Proteus).
- Problematic hospital flora, primarily Pseudomonas aeruginosa (Pseudomonas aeruginosa).
- Pathogens of respiratory and neuroinfections: Haemophilus influenzae (Haemophilus influenzae), meningococci (Neisseria meningitidis).
- Pathogen of gonorrhea: gonococci (Neisseria gonorrhoeae).
At the same time, the drug is completely devoid of activity against gram-positive bacteria and any anaerobes (including Bacteroides).
Such strict selectivity is explained by interaction with bacterial enzymes. Aztreonam exhibits high resistance to $\beta$-lactamases produced by gram-negative flora. However, enzymes produced by gram-positive microorganisms and bacteroides easily destroy the monocyclic ring of the antibiotic, rendering it ineffective against these pathogens.
Clinical pharmacology and indications
In clinical practice, aztreonam has the status of a reserve drug. The key indication for choosing this antibiotic is the need to treat severe infections in patients with confirmed, severe allergy to penicillins (due to low cross-allergenicity).
The drug is used for a wide range of pathologies, as well as in cases of failure of other antibiotics:
- Infectious lesions of the lower respiratory tract (including nosocomial pneumonia).
- Intra-abdominal infections and pelvic inflammatory disease.
- Severe urinary tract infections.
- Purulent-inflammatory processes of the skin, soft tissues, as well as bone and joint infections.
- 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 frequency of administration is every 8–12 hours.
Aztreonam therapy may be accompanied by a number of side effects:
- Gastrointestinal tract: various dyspeptic disorders.
- Allergic manifestations: skin reactions.
- Central nervous system: headache.
- Local reactions: development of phlebitis at the site of intravenous administration.
It is easy to remember aztreonam's spectrum by the rule of "Three NOs": NO gram-positive bacteria, NO anaerobes, NO cross-allergy with penicillins. It targets only gram-negative flora.
Class and exam questions
Why doesn't aztreonam work against staphylococci and streptococci?
Its monocyclic $\beta$-lactam ring is rapidly destroyed by $\beta$-lactamases, which are actively produced by gram-positive bacteria.
Can aztreonam be prescribed to patients with penicillin anaphylaxis?
Yes, this is one of the main indications. Due to its chemical structure, aztreonam has extremely low cross-allergenicity with classical penicillins.
Is aztreonam effective for Pseudomonas infection?
Yes, Pseudomonas aeruginosa is within its spectrum of high antimicrobial activity, making it an important drug for nosocomial infections.
How is the drug administered?
Aztreonam is administered only parenterally (intravenously or intramuscularly) every 8–12 hours.
What else to study on this topic
- Resistance mechanisms: how $\beta$-lactamases of gram-positive bacteria and bacteroides work
- Nosocomial pneumonia: the place of monobactams in modern therapy regimens
- Specifics of treating generalized infections (sepsis, meningitis) caused by Pseudomonas aeruginosa
- Comparative characteristics of monocyclic and bicyclic $\beta$-lactams
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