Beta-lactams are one of the more commonly used antibiotics in rhinosinusitis. Amoxicillin with or without clavulanate and less commonly third-generation cephalosporins are often used in CRS. Depending on local resistance patterns that vary from region to region, amoxicillin has fair activity against common sinusitis pathogens such as Streptococcus pneumoniae, Moraxella catarrhalis, and Haemophilus influenzae [51]. Both beta-lactamase and penicillin-binding protein resistance patterns have been documented with amoxicillin, however, and the addition of a beta-lactamase inhibitor like clavulanate improves the coverage against agents such as H. influenzae, M. catarrhalis, and S. aureus [52]. In the case of S. pneumoniae resistance, which is based on penicillin-binding protein changes, resistance can be overcome by higher amoxicillin serum levels. The commonly used adult amoxicillin dosages are usually sufficient [53].

Second- and third-generation cephalosporins have increased activity against H. influenza and gram-negative aerobes. Third-generation cephalosporins generally have very good activity against M. catarrhalis and H. influenzae, with fair activity against S. pneumoniae [51]. No oral cephalosporins are active against Pseudomonas aeruginosa.

Macrolides are frequently prescribed in CRS due to the anti-infective and anti-inflammatory properties. Macrolides used in CRS include azithromycin, clarithromycin, and erythromycin. Their greatest antimicrobial property is against streptococci, staphylococci, and other gram-positive pathogens, but also against atypical microbes such as Mycoplasma pneumoniae. Similarly to beta-lactams, S. pneumoniae resistance is an increasing problem and has reached rates over 20 % in many European countries [54].

Fluoroquinolones have gained common use in CRS for their broad spectrum of activity, but more importantly for their coverage of P. aeruginosa and other gram-negative bacteria. This group covers many gram-positive agents well, specifically H. influenzae, M. catarrhalis, and S. pneumoniae. The agents in this group used for CRS most commonly are levofloxacin, ciprofloxacin, and moxifloxacin. Ciprofloxacin and levofloxacin generally have the best activity against P. aeruginosa and the least against gram-positives [55]. Therefore, ciprofloxacin and levofloxacin should be thoughtfully used and possibly reserved for P. aeruginosa.

Doxycycline is an agent whose use can be helpful in CRS because of its activity against methicillin-resistant S. aureus. The effectiveness of this drug against MRSA depends on local resistance rates, but is generally over 80 % [56]. This drug also has good coverage of atypical microbes like Mycoplasma pneumonia.