Group B streptococcal infection medical therapy

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Rim Halaby, M.D. [2]

Overview

Group B streptococcal (GBS) infection should be suspected as a causative agent for bacterial meningitis in infants less than two years of age, among whom empirical antibiotic therapy should be initiated immediately. Ampicillin or penicillin are recommended for the treatment of confirmed neonatal GBS meningitis. Intrapartum antibiotic treatment should be administered to asymptomatic pregnant women who are carriers of GBS because it provides prophylaxis against the transmission of the infection to the neonate. Penicillin remains the agent of choice for intrapartum antibiotic prophylaxis, with ampicillin as an acceptable alternative. Penicillin and ampicillin are generally effective for the treatment of GBS infection in non-pregnant adults.

Medical Therapy in Neonatal Meningitis

Empirical Antibiotic Therapy in Neonatal Meningitis

Group B streptococcal (GBS) infection should be suspected as a causative agent for bacterial meningitis in infants less than two years of age, among whom empirical antibiotic therapy should be initiated immediately according to the Infectious Diseases Society of America (IDSA) guidelines.

Shown below is a table summarizing the choice of empirical medical therapy in neonatal meningitis.

Age	Possible pathogens causing the bacterial meningitis	Empirical treatment
< 1 month	Streptococcus agalactiae Escherichia coli Listeria monocytogenes Klebsiella	Ampicillin + cefotaxime OR Ampicillin + aminoglycoside
1-23 months	Streptococcus pneumoniae Neisseria meningitidis Streptococcus agalactiae Haemophilus influenzae E. coli	Vancomycin + third generation cephalosporin

Targeted Antibiotic Therapy in GBS Neonatal Meningitis

Shown below is a table summarizing the choice of targeted medical therapy in neonatal meningitis according to the IDSA guidelines.

Recommended therapy for GBS meningitis	Alternative therapy for GBS meningitis
Ampicillin OR Penicillin Consider adding an aminoglycoside	Third generation cephalosporin (Ceftriaxone or cefotaxime)

Recommended Dosage of Antibiotics

Shown below is a table summarizing the recommended dosage of antibiotics according to the IDSA guidelines.

Antibiotic agent	Dosage
Amikacin	0-7 days: 15-20 mg/kg 8-28 days: 30 mg/kg Infants > 28 days: 20-30 mg/kg
Ampicillin	0-7 days: 150 mg/kg 8-28 days: 200 mg/kg Infants > 28 days: 300 mg/kg
Cefotaxime	0-7 days: 100-150 mg/kg 8-28 days: 150-200 mg/kg Infants > 28 days: 225-300 mg/kg
Ceftazidime	0-7 days: 100-150 mg/kg 8-28 days: 150 mg/kg Infants > 28 days: 150 mg/kg
Ceftriaxone	Infants > 28 days: 80-100 mg/kg
Gentamicin	0-7 days: 5 mg/kg 8-28 days: 7.5 mg/kg Infants > 28 days: 7.5 mg/kg
Penicillin G	0-7 days: 0.15 mg/kg 8-28 days: 0.2 mg/kg Infants > 28 days: 0.3 mg/kg
Tobramycin	0-7 days: 5 mg/kg 8-28 days: 7.5 mg/kg Infants > 28 days: 7.5 mg/kg
Vancomycin	0-7 days: 20-30 mg/kg 8-28 days: 30-45 mg/kg Infants > 28 days: 60 mg/kg

Consider lower dosages and longer intervals of antibiotics in case of very low-birth weight neonates.

Medical Therapy for Pregnant Women

Asymptomatic Carriers

Treatment for GBS is indicated in cases of:

• GBS bacteriuria during any trimester of the current pregnancy
• Positive GBS vaginal-rectal screening culture in late gestation during current pregnancy

Intrapartum antibiotic treatment of asymptomatic pregnant women who are carriers of GBS is recommended because it provides prophylaxis against the transmission of the infection to the newborn.

Intrapartum antibiotic prophylaxis is not indicated in this circumstance if a cesarean delivery is performed before onset of labor on a woman with intact amniotic membranes.

The following are key components of intrapartum antibiotic prophylaxis agents and dosing:

• Penicillin remains the agent of choice for intrapartum antibiotic prophylaxis, with ampicillin as an acceptable alternative (class A, level of evidence I).

• Penicillin-allergic women who do not have a history of anaphylaxis, angioedema, respiratory distress, or urticaria following administration of a penicillin or a cephalosporin should receive cefazolin (class B, level of evidence II).

• Antimicrobial susceptibility testing should be ordered for antenatal GBS cultures performed on penicillin-allergic women at high risk for anaphylaxis because of a history of anaphylaxis, angioedema, respiratory distress, or urticaria following administration of a penicillin or a cephalosporin (AII). To ensure proper testing, clinicians must inform laboratories of the need for antimicrobial susceptibility testing in such cases (class A, level of evidence III).

• Penicillin-allergic women at high risk for anaphylaxis should receive clindamycin if their GBS isolate is susceptible to clindamycin and erythromycin, as determined by antimicrobial susceptibility testing; if the isolate is sensitive to clindamycin but resistant to erythromycin, clindamycin may be used if testing for inducible clindamycin resistance is negative (CIII). Penicillin-allergic women at high risk for anaphylaxis should receive vancomycin if their isolate is intrinsically resistant to clindamycin as determined by antimicrobial susceptibility testing, if the isolate demonstrates inducible resistance to clindamycin, or if susceptibility to both agents is unknown (class C, level of evidence III).

• The recommended dosing regimen of penicillin G is 5 million units intravenously, followed by 2.5--3.0 million units intravenously every 4 hours (class A, level of evidence II). The range of 2.5--3.0 million units is recommended to achieve adequate drug levels in the fetal circulation and amniotic fluid while avoiding neurotoxicity. The choice of dose within that range should be guided by which formulations of penicillin G are readily available in order to reduce the need for pharmacies to specially prepare doses.

Shown below is an algorithm depicting the choice of antibiotics for the primary prevention of early-onset GBS neonatal infection based on the 2010 revised CDC guidelines.

Is the patient allergic to penicillin?

No

Yes

Penicillin G, 5 million units IV initial dose, then 2.5-3.0 million units every 4 hours until delivery OR Ampicillin, 2 g IV initial dose, then 1 g IV every 8 hours until delivery

Does the patient a history of any of the following after receiving penicillin or cephalosporin? Anaphylaxis Angioedema Respiratory distress Urticaria

No

Yes

Cefazolin, 2 g IV initial dose, then 1 g IV every 8 hours until delivery

Is the isolate susceptible to clindamycin and erythromycin?

No

Yes

Vancomycin, 1 g IV every 12 hours until delivery

Clindamycin, 900 mg IV every 8 hours until delivery

Chorioamnionitis

The treatment of chorioamnionitis requires the immediate administration of broad spectrum antibiotics until delivery. In addition, antipyretics must be administered.

The broad spectrum antibiotics regimen, particularly among pregnant women who were administered prophylactic intrapartum penicillin G for GBS, includes:

• Ampicillin 2 g every 6 hours, PLUS
• Gentamicin 1.5 mg/kg every 8-24 hours

If the patient is undergoing C-section, the following antibiotics must be added to the initial broad spectrum antibiotics to cover for anaerobes:

• Clindamycin 900 mg IV, OR
• Metronidazole 500 mg IV

Medical Therapy in Adults

Penicillin and ampicillin are generally effective for the treatment of GBS infection in non pregnant adults; however, it is best that the antibiotic treatment is guided by the susceptibility testing results. The duration of antibiotic therapy should be a minimum of 2 weeks but longer duration of treatment should be attempted in fulminant infections.

Gentamicin might be considered as an addition to the initial antibiotic regimens.

The dose of antibiotics might be higher than that in other types of infection, particularly in meningitis.

References

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