Pharyngitis Strep Throat

The primary use of antibiotics in pharyngitis is to treat infection due to group A Streptococcus (GAS). GAS is the most common bacterial agent causing acute pharyngitis, and accounts for approximately 15% to 30% of cases in children and 5% to 10% of adults (44,45). However, streptococcal pharyngitis is difficult to differentiate from other causes (such as viral etiology) on clinical grounds (45).

Definitive diagnosis of streptococcal pharyngitis is based on the identification of GAS in the throat by culture, rapid antigen detection test, or by serologic means. Results of culture and serologic testing are not available at the time of clinical decision making and are therefore not timely. Rapid antigen detection test provides the result to the clinician within minutes. However, the sensitivity varies from 60% to 90%; thus, a false test does not rule out the diagnosis.

Intramuscular penicillin and oral penicillin V or oral amoxicillin continue to be the recommended first-line drugs by most guideline. Table 6 shows the most recent antimicrobial agents recommended for the treatment of streptococcal pharyngitis (46). GAS continues to be highly sensitive to penicillin and amoxicillin and these agents have been the first-line recommended therapy. In patients with penicillin allergy, an oral cephalosporin or a macrolide is recommended. An oral cephalosporin may be used in patients who do not have immediate-type hyper-sensitivity to beta-lactam agents. Macrolide antibiotic may be used in those patients who are allergic to penicillin regardless of the type of reaction. However, the increasing resistance of GAS to macrolides worldwide is of major concern (47). Macrolide resistance may reside in the erm gene or mef gene. Cross-resistance to all the macrolide antibiotics is the rule. Streptococci with low level of macrolide resistance are commonly associated with the mef gene that is responsible for the efflux of the antibiotic out of the bacterial cells. These bacteria are usually susceptible to clindamycin. Streptococci that are highly macrolide resistant are usually not susceptible to clindamycin as well, and the erm gene commonly mediates this resistance.

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