Strep throat is medical condition brought on by an infection of streptococcus bacteria, and results in sore throat, fever, and swollen lymph nodes. Amoxicillin is an antibiotic often used to treat strep, but its usefulness against strep infections is now being questioned. Recent reviews of the efficacy of amoxicillin for strep have shown that amoxicillin fails to cure the infection in about two out of every ten people treated for a strep infection. When amoxicillin fails, the result is a prolonged infection and the need for a second course of a different antibiotic.
Antibiotics are almost always used to treat strep throat because strep throat is an infection cause only by bacteria, not a virus, and its presence is easily detected by a rapid test. In addition, antibiotic treatments for strep have traditionally decreased the duration and severity of the infection and often thwarted secondary complications, such as sinus and ear infections. Using penicillin and amoxicillin for strep treatment was, in the past, a good and effective choice, but now both antibiotics are becoming progressively inadequate. The reason for the failure of amoxicillin for strep does not seem to be the development of a strep bacterial strain which is resistant to amoxicillin.
Two possible theories may explain the occasional ineffectiveness of amoxicillin for strep. Previously, strep bacteria were thought to exist only outside of cells, but recent studies have shown this to be untrue. It is now known that strep bacteria are sometimes able to penetrate and survive inside the upper respiratory tract cells. Since amoxicillin is not able to penetrate the cell membrane, it cannot come in contact with the bacteria to destroy it. In cases where the strep bacteria has penetrated the throat cells, it can withstand the amoxicillin treatment.
In a second explanation, strep bacteria co-colonize with other bacteria, which are resistant to amoxicillin, and may allow strep to adhere to the throat more easily. These particular florae are able to secrete a chemical, called beta-lactamase, which can inactivate amoxicillin. By co-colonizing, the strep bacteria, although not drug resistant itself, can benefit from the resistant mechanisms used by neighboring bacteria. Not everyone is has these special bacteria, so in some cases amoxicillin for strep is still useful. If these special bacteria are present in the throat, it may explain the failure of amoxicillin for strep treatment.
With this new information, the guidelines for the treatment of strep are changing. Cephalexin, cephalosporin, or azithromycin are now often prescribed for a strep infection. Amoxicillin is still used to treat pneumonia, sinus infections, and ear infections.
