monobaktam

Monobaktam refers to a subclass of beta-lactam antibiotics that contain a single monocyclic beta-lactam ring and lack the fused rings found in penicillins and cephalosporins. The clinically important member of this class is aztreonam. Monobactams inhibit bacterial cell wall synthesis by binding to penicillin-binding proteins, yielding bactericidal activity.

Spectrum and use: Monobactams show activity predominantly against Gram-negative aerobic bacteria, including many Enterobacterales and Pseudomonas aeruginosa. They have limited or no activity against most Gram-positive organisms and anaerobes. Aztreonam is used for systemic infections and is also formulated for inhalation to treat Pseudomonas infections in cystic fibrosis patients. Because of their beta-lactam structure, monobactams are often considered safe in patients with penicillin allergy, though cross-reactivity is not zero.

Pharmacology and pharmacokinetics: Monobactams are usually administered intravenously or intramuscularly; an inhaled form of aztreonam is available for pulmonary infections. They are primarily eliminated renally, so dose adjustments are needed in renal impairment.

Resistance and limitations: Bacterial resistance can arise through beta-lactamase production, changes in penicillin-binding proteins, or reduced permeability. Some beta-lactamases, including certain metallo-beta-lactamases, can inactivate aztreonam. Because of their narrow spectrum, monobactams are typically used when Gram-negative activity is required and Gram-positive or anaerobic coverage is unnecessary.

Safety: Adverse effects are usually mild and may include gastrointestinal symptoms, rash, or hypersensitivity reactions. High doses or renal dysfunction can increase the risk of seizures.