From the Guidelines
Antibiotics can be broadly classified into several major classes, each with distinct mechanisms of action and spectrums of activity, including penicillins, cephalosporins, carbapenems, monobactams, aminoglycosides, fluoroquinolones, macrolides, tetracyclines, lincosamides, glycopeptides, oxazolidinones, polymyxins, and miscellaneous agents. When teaching PA students, it's essential to break down these classes and their spectrum of activity to ensure they understand how to select the most appropriate antibiotic for a given infection. The classes and their spectrums can be summarized as follows:
- Penicillins: target gram-positive organisms, with extended-spectrum penicillins and those combined with beta-lactamase inhibitors covering more gram-negative bacteria 1
- Cephalosporins: divided into generations, with first-generation primarily for gram-positives, second-generation with improved gram-negative coverage, third-generation with enhanced gram-negative activity, and fourth/fifth-generation with broader spectrum including MRSA for ceftaroline
- Carbapenems: offer the broadest coverage including many resistant organisms
- Monobactams: specifically target aerobic gram-negatives
- Aminoglycosides: effective against gram-negatives and work synergistically with other antibiotics
- Fluoroquinolones: include respiratory and urinary agents with gram-negative and some gram-positive coverage
- Macrolides: target atypical organisms and some gram-positives
- Tetracyclines and glycylcyclines: have broad-spectrum activity including atypicals
- Lincosamides: cover gram-positives and anaerobes
- Glycopeptides and lipoglycopeptides: target resistant gram-positives
- Other important classes include oxazolidinones for resistant gram-positives, polymyxins for multidrug-resistant gram-negatives, and miscellaneous agents like metronidazole for anaerobes, trimethoprim-sulfamethoxazole for various pathogens, and nitrofurantoin for urinary tract infections. Some key points to note from the evidence include the recommendation for specific antimicrobial therapy for certain pathogens, such as penicillin G or amoxicillin for Streptococcus pneumoniae, and the use of fluoroquinolones or azithromycin for Legionella species 1. Understanding these classifications and spectrums of activity is crucial for clinicians to select appropriate empiric therapy based on likely pathogens and local resistance patterns, as highlighted in the guidelines for the management of community-acquired pneumonia in adults 1.
From the Research
Antibiotic Classes
- Fluoroquinolones: broad-spectrum antibiotics, effective against both Gram-positive and Gram-negative bacteria 2, 3, 4
- Macrolides: effective against Gram-positive bacteria, and some Gram-negative bacteria, with a unique mechanism of action that can attenuate the production of pneumolysin by Streptococcus pneumoniae 5
- Penicillins: effective against Gram-positive bacteria, with amoxicillin being a commonly used agent 2
- Cephalosporins: broad-spectrum antibiotics, effective against both Gram-positive and Gram-negative bacteria, with ceftriaxone being a commonly used agent 3, 4
- Aminoglycosides: effective against Gram-negative bacteria, with tobramycin being a commonly used agent 5
Spectrum of Activity
- Levofloxacin: broad-spectrum antibiotic, effective against Streptococcus pneumoniae, Gram-negative bacteria, and non-pseudomonas Gram-negative pathogens 2, 3, 4
- Amoxicillin/Clavulanate: effective against Streptococcus pneumoniae, and some Gram-negative bacteria 2
- Azithromycin: effective against Streptococcus pneumoniae, and some Gram-negative bacteria, with a unique mechanism of action that can attenuate the production of pneumolysin by Streptococcus pneumoniae 3, 4
- Ceftriaxone: broad-spectrum antibiotic, effective against Streptococcus pneumoniae, and Gram-negative bacteria 3, 4
- Doxycycline: effective against some Gram-positive and Gram-negative bacteria, with a unique mechanism of action that can affect the production of pneumolysin by Streptococcus pneumoniae 5