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Shigella Infection Medication

  • Author: Jaya Sureshbabu, MBBS, MRCPCH(UK), MRCPI(Paeds), MRCPS(Glasg), DCH(Glasg); Chief Editor: Russell W Steele, MD  more...
Updated: Jun 28, 2016

Medication Summary

Various antimicrobial agents are effective in the treatment of shigellosis, although options are becoming limited because of globally emerging drug resistance. Resistance of Shigella species to sulfonamides, tetracyclines, ampicillin, and trimethoprim-sulfamethoxazole (TMP-SMX) has been reported worldwide, and these agents are not recommended as empirical therapy.

The World Health Organization (WHO) recommends that all suspected cases of shigellosis based on clinical features be treated with effective antimicrobials (antibiotics).[18] The choice of antimicrobial drug has changed over the years as resistance to antibiotics has occurred, with different patterns of resistance being reported around the world. Evidence is insufficient to consider any class of antibiotic superior in efficacy in treating Shigella dysentery. The following antibiotics are used to treat Shigella dysentery:

  • Beta-lactams: Ampicillin, amoxicillin, third-generation cephalosporins (cefixime, ceftriaxone), and pivmecillinam (not available in the United States)
  • Quinolones: Nalidixic acid, ciprofloxacin, norfloxacin, and ofloxacin
  • Macrolides: Azithromycin
  • Others: sulfonamides, tetracycline, cotrimoxazole, and furazolidone.

Most clinical infections with S sonnei are self-limited (48-72 h) and may not require antimicrobial therapy.

If an ampicillin and TMP-SMX resistant strain is isolated or if susceptibility is unknown, parenteral ceftriaxone sodium, fluoroquinolone (eg, ciprofloxacin, ofloxacin), azithromycin dihydrate (off-label indication), or oral cefixime are the drugs of choice.[8, 19, 20] Amoxicillin is less effective than ampicillin for treatment of ampicillin-sensitive strains. Oral first- and second-generation cephalosporins are inadequate despite in vitro susceptibility. Recently, Shigella isolates with decreased susceptibility to azithromycin (DSA-Shigella), with minimum inhibitory concentration (MIC) greater than 16 µ g/mL has been described by the CDC.[21]

In June 2015, the Centers for Disease Control and Prevention (CDC) warned that they received reports of infections with Shigella strains that are not susceptible to ciprofloxacin and/or azithromycin.  CDC is seeing resistance to ciprofloxacin in 1.6% of the Shigella cases tested and resistance to azithromycin in approximately 3%. The CDC added that most cases have been reported among gay, bisexual, and other men who have sex with men in Illinois, Minnesota, and Montana and among international travelers, but cases are also occurring among other populations.[22, 23, 24]

Because shigellosis is self-limiting, some authorities recommend withholding antibiotic therapy. When an effective antibiotic is given, clinical improvement is anticipated within 48 hours. This lessens the risk of serious complications and death, shortens the duration of symptoms, and hastens the elimination of Shigella and the subsequent spread of infection. The risk of continued shedding of organisms in stool increases the risk of transmission of further disease among contacts argues against withholding antimicrobial treatment.[25]

Antimicrobial therapy is typically administered for 5 days. Antibiotic treatment decreases the duration of illness, person-to-person spread, and cases in household contacts. Treatment in malnourished children (eg, in developing countries) is likely to reduce the risk of worsening malnutrition morbidity after shigellosis. In persons infected with S dysenteriae type 1, early administration of effective antibiotics decreases Shiga toxin (Stx) concentrations in the stool and lowers HUS risk. However, the risk of HUS caused by E coli O157-H7 may be increased with the early administration of antibiotics. Prophylactic antibiotics are not recommended for contacts.

Antidiarrheal medications (diphenoxylate hydrochloride with atropine [Lomotil] or loperamide [Imodium]) should not be used because of the risk of prolonging the illness. WHO has introduced the use of zinc for 10-14 days as part of a diarrheal disease control program in addition to oral rehydration therapy. Initiating zinc at the time of diarrhea leads to shorter duration and fewer loose stools.[17, 26]

A child with typical dysentery that responds to initial empirical antibiotic treatment should continue taking the same drug for a full 5-day course, even if the stool culture is negative.

Immunity and vaccination

Once someone has had Shigella infection, they are not likely to become infected with that specific type again for at least several years. However, they can still become infected with other types of Shigella. Presumably, this immunity could be due to secretory IgA. Circulating antibodies can be detected in immune individuals.

Presently, no US Food and Drug Administration (FDA)–approved vaccines are available. However, research is underway to develop live oral vaccines to prevent shigellosis.[27, 28] Three approaches to Shigella vaccine development that are under active investigation are (1) parenteral O–specific polysaccharide conjugate vaccine, (2) nasal proteasomes delivering Shigella lipopolysaccharide, and (3) live attenuated invasive Shigella deletion mutants that are administered orally.

Researchers have launched an early-stage human clinical trial of two related candidate vaccines to prevent infection with Shigella. The trial is being conducted at the Cincinnati Children’s Hospital Medical Center, one of the eight NIAID-funded Vaccine and Treatment Evaluation Units in the United States funded by the National Institute of Allergy and Infectious Diseases (NIAID).[29]



Class Summary

Ampicillin and TMP-SMZ are effective for susceptible strains; amoxicillin is less effective than this because of its rapid absorption high in the GI tract. The oral route is preferred except for seriously ill patients. In the United States, sentinel surveillance data from 2003-2006 indicated that 94% of S sonnei and 67% of S flexneri organisms were resistant to ampicillin and TMP-SMZ. The WHO now recommends that clinically diagnosed cases of Shigella dysentery be treated with ciprofloxacin as first line treatment, and pivmecillinam (not available in the United States), ceftriaxone, or azithromycin as second line treatment and lists the others as ineffective (WHO 2005a).[30] . However, resistance to quinolones has also been observed since the late 1990s, and some authors have questioned the effectiveness of this class for Shigella. The choice of antibiotic to use as first line against Shigella dysentery should be governed by periodically updated local antibiotic sensitivity patterns of Shigella isolates.

Ciprofloxacin (Cipro)


First-line treatment for shigellosis. Fluoroquinolone that inhibits bacterial DNA synthesis and, consequently, growth, by inhibiting DNA gyrase and topoisomerases, which are required for replication, transcription, and translation of genetic material. Quinolones have broad activity against gram-positive and gram-negative aerobic organisms. Has no activity against anaerobes. Continue treatment for total of 5 days, even empirical treatment in patient with typical bloody diarrhea who responds clinically with negative stool culture. (7-14 d typical)

Ceftriaxone (Rocephin)


Third-generation cephalosporin with broad-spectrum, gram-negative activity; lower efficacy against gram-positive organisms; higher efficacy against resistant organisms. Bactericidal activity results from inhibiting cell wall synthesis by binding to one or more penicillin binding proteins. Exerts antimicrobial effect by interfering with synthesis of peptidoglycan, a major structural component of bacterial cell wall. Bacteria eventually lyse due to the ongoing activity of cell wall autolytic enzymes while cell wall assembly is arrested.

Highly stable in presence of beta-lactamases, both penicillinase and cephalosporinase, of gram-negative and gram-positive bacteria. Approximately 33-67% of dose excreted unchanged in urine, and remainder secreted in bile and ultimately in feces as microbiologically inactive compounds. Reversibly binds to human plasma proteins, and binding have been reported to decrease from 95% bound at plasma concentrations < 25 mcg/mL to 85% bound at 300 mcg/mL.

Azithromycin (Zithromax)


Acts by binding to 50S ribosomal subunit of susceptible microorganisms and blocks dissociation of peptidyl tRNA from ribosomes, causing RNA-dependent protein synthesis to arrest. It has enhanced activity against gram-negative organisms. Concentrates in phagocytes and fibroblasts, as demonstrated with in vitro incubation techniques; hence, plasma concentrations are very low but tissue concentrations are very high. It has a long tissue half-life and once daily dosage is recommended. In vivo data suggest that concentration in phagocytes may contribute to drug distribution to inflamed tissues.

Ampicillin (Principen)


Broad-spectrum penicillin. Interferes with bacterial cell-wall synthesis during active replication, causing bactericidal activity against susceptible organisms.

Nalidixic acid (NegGram)


First-generation quinolone. Blocks bacterial DNA gyrase. Useful in patients with sulfas and cephalosporin allergy. WHO guidelines state most Shigella strains are now resistant to nalidixic acid.

Cefixime (Suprax)


Third-generation oral cephalosporin with broad activity against gram-negative bacteria. By binding to one or more of the penicillin-binding proteins, it arrests bacterial cell wall synthesis and inhibits bacterial growth. For outpatient use in drug-resistant Shigella infections.

Trimethoprim and sulfamethoxazole (Bactrim, Cotrim)


Combination effective for shigellosis in the past, but WHO states most Shigella strains are now resistant. Produces sequential blockade in folic acid synthesis. Effect frequently synergistic and bactericidal.


Trace Elements/Metals

Class Summary

WHO has introduced the use of zinc for 10-14 days as part of a diarrheal disease control program in addition to oral rehydration therapy. Initiating zinc at the time of diarrhea leads to shorter duration and fewer loose stools.[17, 26]

Zinc (Galzin, Zinimin, ZnCl2)


Zinc supplementation has been found to decrease duration and severity of diarrheal episodes.

Contributor Information and Disclosures

Jaya Sureshbabu, MBBS, MRCPCH(UK), MRCPI(Paeds), MRCPS(Glasg), DCH(Glasg) Consultant Pediatrician and Neonatologist, PRS Hospital, India

Disclosure: Nothing to disclose.


Poothirikovil Venugopalan, MBBS, MD, FRCPCH Consultant Pediatrician with Cardiology Expertise, Department of Child Health, Brighton and Sussex University Hospitals, NHS Trust; Honorary Senior Clinical Lecturer, Brighton and Sussex Medical School, UK

Poothirikovil Venugopalan, MBBS, MD, FRCPCH is a member of the following medical societies: Royal College of Paediatrics and Child Health, Paediatrician with Cardiology Expertise Special Interest Group, British Congenital Cardiac Association

Disclosure: Nothing to disclose.

Walid Abuhammour, MD, MBA, FAAP Professor of Pediatrics, Michigan State University College of Medicine; Director of Pediatric Infectious Disease, Department of Pediatrics, Al Jalila Children's Hospital

Walid Abuhammour, MD, MBA, FAAP is a member of the following medical societies: American Medical Association, Infectious Diseases Society of America, Pediatric Infectious Diseases Society

Disclosure: Nothing to disclose.

Specialty Editor Board

Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Nothing to disclose.

Larry I Lutwick, MD Professor of Medicine, State University of New York Downstate Medical School; Director, Infectious Diseases, Veterans Affairs New York Harbor Health Care System, Brooklyn Campus

Larry I Lutwick, MD is a member of the following medical societies: American College of Physicians, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Chief Editor

Russell W Steele, MD Clinical Professor, Tulane University School of Medicine; Staff Physician, Ochsner Clinic Foundation

Russell W Steele, MD is a member of the following medical societies: American Academy of Pediatrics, American Association of Immunologists, American Pediatric Society, American Society for Microbiology, Infectious Diseases Society of America, Louisiana State Medical Society, Pediatric Infectious Diseases Society, Society for Pediatric Research, Southern Medical Association

Disclosure: Nothing to disclose.

Additional Contributors

Glenn Fennelly, MD, MPH Director, Division of Infectious Diseases, Lewis M Fraad Department of Pediatrics, Jacobi Medical Center; Clinical Associate Professor of Pediatrics, Albert Einstein College of Medicine

Glenn Fennelly, MD, MPH is a member of the following medical societies: Pediatric Infectious Diseases Society

Disclosure: Nothing to disclose.

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