Author: Brian Holtry

Tetracyclines are the prototypical broad-spectrum antibiotic and are occasionally used as first-line agents in some markets (e.g., Germany) for the treatment of mild acute exacerbations of chronic bronchitis, particularly when cost, penicillin hypersensitivity, and β-lactam resistance are of concern. The widespread use of tetracyclines has resulted in a steady increase in the prevalence of resistance to these agents. Therefore, empiric use of tetracyclines is usually restricted to regions where resistance levels remain low or when other appropriate antibiotics are contraindicated.

Fluoroquinolones are broad-spectrum antibacterials that have experienced an upsurge in use in recent years. Because of their broad-spectrum activity, high efficacy, favorable dosing, and availability in oral and IV form, these agents are indicated for a range of bacterial infections, including respiratory, GI, and urinary tract infections. Earlier generations of fluoroquinolones (e.g., ofloxacin) had limited activity against some respiratory pathogens, such as S. pneumoniae. However, more recent fluoroquinolone agents (so-called third-generation agents or the “respiratory fluoroquinolones”) are active against a broad spectrum of gram-positive and gram-negative bacteria, including atypical organisms.

Moxifloxacin displays excellent activity against a broad spectrum of bacteria, including penicillin- and macrolide-resistant S. pneumoniae.

Ketolides are a new class of macrolide derivatives designed specifically to combat macro fide-resistant respiratory tract pathogens. The ketolides are semisynthetic derivatives of the macrolide erythromycin A, with a keto group replacing the 1-cladinose group at position 3 of the macrolactone ring. The ketolides exhibit good activity against gram-positive and some gram-negative organisms, and have excellent activity against drug-resistant S. pneumoniae, including macrolide-resistant strains.

Macrolides inhibit bacterial protein synthesis. They demonstrate excellent activity against atypical organisms (Mycoplasma, Chlamydia, and Legionella species), but their activity against typical pathogens (H. influenzae and S. pneumoniae) is variable. Macrolides are indicated for use in acute exacerbations of chronic bronchitis and are typically used as first- and second-line agents for this indication.

Carbapenems are penicillin derivatives that have good activity against gram-positive and gram-negative aerobic and anaerobic bacteria. They are highly resistant to β-lactamase and have a very favorable spectrum of activity. A drawback of these agents is that they are available in IV form only.

The cephalosporins contain a basic β-lactam structure fused to a six-membered ring. Drugs in this class differ widely in their spectrum of activity, susceptibility to β-lactamases produced by bacteria, and serum half-life. Cephalosporins are categorized into four generations, with each newer generation representing an improvement in the spectrum of bacterial coverage. First-generation agents have the narrowest spectrum of activity among the cephalosporins.

Cefotaxime is indicated for the treatment of lower respiratory tract infections caused by S. pneumoniae and other streptococci, E. coli, K. pneumoniae and other Klebsiella species, H. influenzae (including ampicillin-resistant strains).

Cefdinir is a third-generation cephalosporin antibiotic used to treat a variety of bacterial infections, including respiratory tract infections, skin infections, and certain ear infections. It works by interfering with bacterial cell wall synthesis, leading to the elimination of harmful bacteria. This antibiotic is known in the for its broad-spectrum activity and is often prescribed when other antibiotics may not be effective.