Antibiotics for Strep Throat (Streptococcal Pharyngitis)

• What is a Strep throat?
• Causes
• Symptoms
• Diagnosis
• Antibiotics for strep throat
• Penicillin
• Amoxicillin

Strep throat, also called streptococcal pharyngitis, is an infection with group A beta-hemolytic streptococcus bacteria.

Strep throat has an incubation period of two to five days and is most common in children 5 to 12 years of age. The illness can occur in clusters and is diagnosed most often in the winter and spring.

While the terms sore throat, tonsillitis, and "strep" are used interchangeably, there are essential differences between these conditions.

Strep throat is caused by Group A beta-hemolytic streptococci which are ordinarily spread by direct person-to-person contact, most likely through droplets of saliva or nasal secretions.

The most common symptoms of strep throat are:

• sore throat
• high temperature, usually over 38°C (101°F)
• swollen lymph glands in the neck
• white or yellow spots on the tonsils or back of throat
• fever and chills
• headache
• stomach-ache (especially in children)

Indicators that increase or decrease the likelihood of strep throat
Increased likelihood	Decreased likelihood
Age 3-14 years	Age 45 years or older
High fever (> 38 °C)	Afebrile
Absence of a cough	Cough
Exudative pharyngitis or tonsillitis	Stuffy, runny nose; conjunctivitis
Anterior cervical adenitis	Hoarseness
Current group A strep epidemic	Discrete oral ulcerative lesions
Recent close exposure to group A strep	Diarrhea

Because many of the signs and symptoms of streptococcal pharyngitis are non-specific it is recommended that the clinical diagnosis is confirmed with laboratory tests. Throat cultures are the conventional gold standard method for confirming the diagnosis.

Antibiotics should not be prescribed until the culture result confirms strep throat or another bacterial pathogen. Antibiotic treatment can begin immediately only when:

• Patient is very ill
• Culture results will be delayed for more than 72 hours
• Patient follow-up will be difficult

Antibiotics should be discontinued if the culture result is negative.

Antibiotics are commonly used to treat strep throat because they:

• Kill the bacteria and shorten the time the patient is contagious. The patient usually is no longer contagious 24 to 48 hours after starting antibiotics.
• Prevent rare complications. Although uncommon, strep bacteria can spread to other parts of the body causing ear or sinus infections or an abscess behind or around the tonsils (peritonsillar abscess). Antibiotics may also prevent the infection from triggering immune system to attack itself and cause serious conditions such as rheumatic fever.
• Relieve discomfort and speed healing to some degree.

Antibiotic selection requires consideration of patient allergies, bacteriologic and clinical efficacy, frequency of administration, duration of therapy, potential side effects, compliance and cost.

Since its introduction in the 1940s, penicillin has been the “gold standard” antibiotic for strep throat and still remains the drug of choice in many cases of strep throat. The ability of penicillin to kill group A streptococci has not changed in more than 50 years. There has never been a group A streptococcus grown from a person that has been resistant to penicillin.

Penicillin has proven efficacy and safety. It is a narrow-spectrum agent that does not promote antimicrobial resistance.

Penicillin V dosage:

• Children: 250 mg two or three times daily for 10 days
• Adults: 500 mg two or three times for daily 10 days

Amoxicillin, a broader spectrum penicillin, may have some advantages because of higher blood levels, longer plasma half life, and lower protein binding activity. Suspensions of this drug taste better than penicillin V suspensions, and chewable tablets are available. However, gastrointestinal side effects and skin rash may be more common with amoxicillin.

Amoxicillin has no microbiologic advantage over the less expensive penicillin. Some studies show that amoxicillin given just once a day may work as well as penicillin V given more often.

Amoxicillin dosage:

• Children: 40 mg/kg per day in three divided doses for 10 days
• Adults: 500 mg three times daily for 10 days

Amoxicillin/Clavulanate Potassium (Augmentin) is resistant to degradation from beta-lactamase produced by pathogens that may colonize the tonsils and pharynx. Amoxicillin-clavulanate is often used to treat recurrent streptococcal pharyngitis. Its major adverse effect is diarrhea. Also it is expensive.

Amoxicillin/Clavulanate Potassium dosage:

• Children: 40 mg/kg per day, in two or three divided doses for 10 days
• Adults: 500 to 875 mg two times daily for 10 days

Alternative antibiotics must be used in patients with penicillin allergy, poor compliance or penicillin treatment failure. Patients who do not respond to initial treatment should be treated with antibiotic that is not inactivated by penicillinase-producing organisms (e.g., amoxicillin-clavulanate potassium, a cephalosporin or a macrolide).

Azithromycin is one of the most widely studied antibiotics for the treatment of group A beta-hemolytic streptococcus (GABHS) infections. Azithromycin has the advantage of simple and short dosing regimen. Also, new macrolide azithromycin has a similar effectiveness to old erythromycin but may cause less gastrointestinal side effects.

Azithromycin can be taken once daily and produces high tonsillar tissue concentrations. A 5-day course of azithromycin is approved by the FDA as a second-line therapy for the treatment of individuals 16 years of age or older with group A streptococcus pharyngitis. The recommended dosage is 500 mg as a single dose on the first day, followed by 250 mg once daily for 4 days 1.

For children a total dose of 60 mg/kg azithromycin given during 3 or 5 days (12 mg/kg once daily for 5 days or 20 mg/kg once daily for 3 days) provides an alternative treatment in cases of penicillin hypersensitivity, when patient is unwilling to a 10-day regimen or for patients who fail therapy with penicillin antibiotics2.

Azithromycin dosage:

• Children: 12 mg per kg for 5 days once daily for 5 days
• Adults: 500 mg on day 1; 250 mg once daily on days 2 through 5

Several studies indicate that a 10-day course of a cephalosporin is superior to penicillin in eradicating group A beta-hemolytic streptococci5.

It is thought that narrower-spectrum cephalosporins such as cefadroxil or cephalexin are probably preferable to the broader-spectrum cephalosporins such as cefaclor, cefuroxime, cefixime, and cefpodoxime.

Cephalexin dosage:

• Children: 25 to 50 mg/kg per day in two to four divided doses for 10 days
• Adults: 500 mg two times daily for 10 days

Currently, the recommended course of cefuroxime for strep throat is 10 days. However, clinical studies6-7 have demonstrated that short-course (4-5 day) treatment with cefuroxime axetil is also very effective in eradicating the infection and preventing post-streptococcal sequelae.

Also, studies have demonstrated that short course of cefuroxime axetil (20 mg/kg/day (max. 500 mg) in two divided doses for 5 days) is effective treatment for children aged 1-17 years with streptococcal tonsillopharyngitis 6.

Cefuroxime axetil dosage:

• Adolescents and adults (13 years and older): 250 mg two times daily for 10 days

Cefdinir is an extended-spectrum oral cephalosporin with potent antistreptococcal activity. The FDA has approved the use of a 5-day course of Cefdinir for the treatment of streptococcal pharyngitis. 5-day course of Cefdinir is equal to the standard 10-day treatment with penicillin V3. However, Cefdinir provides a slightly higher eradication rate of group A streptococcus bacteria.

• 1. Hooton TM. A comparison of azithromycin and penicillin V for the treatment of streptococcal pharyngitis. Am J Med. 1991 Sep 12;91(3A):23S-26S. PubMed
• 2. Cohen R, Reinert P, De La Rocque F, Levy C, Boucherat M, Robert M, Navel M, Brahimi N, Deforche D, Palestro B, Bingen E. Comparison of two dosages of azithromycin for three days versus penicillin V for ten days in acute group A streptococcal tonsillopharyngitis. Pediatr Infect Dis J. 2002 Apr;21(4):297-303. PubMed
• 3. Tack KJ, Henry DC, Gooch WM, Brink DN, Keyserling CH. Free in PMC Five-day cefdinir treatment for streptococcal pharyngitis. Cefdinir Pharyngitis Study Group. Antimicrob Agents Chemother. 1998 May;42(5):1073-5. PubMed
• 4. Cynthia S. Hayres, Harold Willamson JR. Management of Group A Beta-Hemolytic Streptococcal Pharyngitis. American Family Physician Vol. 63/No. 8 (April 15, 2001)
• 5. Casey JR, Pichichero ME. Meta-analysis of cephalosporin versus penicillin treatment of group A streptococcal tonsillopharyngitis in children. Pediatrics. 2004 Apr;113(4):866-82. PubMed
• 6. Scholz H. Streptococcal-A tonsillopharyngitis: a 5-day course of cefuroxime axetil versus a 10-day course of penicillin V. results depending on the children's age. Chemotherapy. 2004 Apr;50(1):51-4.
• 7. Adam D, Scholz H, Helmerking M. J Antimicrob Chemother. 2000 Feb;45 Suppl:23-30.

Published: January 20, 2009
Last updated: May 17, 2011