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Treatment

The clinical significance of Blastocystis spp. is controversial.

Treatment with metronidazole* at various doses has been reported, for example (adults):

  • 250 mg to 750 mg metronidazole* orally 3 times daily for 10 days
  • 1500 mg metronidazole* orally once daily for 10 days

Note: Lack of response to metronidazole has been noted in some areas (Yakoob et al., Br J Biomed Sci 2004;61:75).

Treatment with trimethoprim (TMP)*/sulfamethoxazole (SMX)* at various doses has been reported, for example (adults):

  • 6 mg/kg TMP*, 30 mg/kg SMX* once daily for 7 days
  • 320mg TMP*, 1600 mg SMX* once daily for 7 days
  • 160 mg TMP*, 800 mg SMX* twice daily for 7 days

Treatment with nitazoxanide* has been shown to be effective in clearing organisms and improving symptoms at the following doses:

  • Adults, 500 mg nitazoxanide* orally twice daily for 3 days.
  • Children, 200 mg nitazoxanide* orally twice daily for 3 days in patients aged 4–11 years, and 100 mg nitazoxanide* orally twice daily for 3 days in patients aged 1–3 years.

Tinidazole*, paromomycin*, iodoquinol*, and ketoconazole* have also been used for clearing Blastocystis, as presented in case reports or small series (see references).

*Not FDA-approved for this indication.

Metronidazole

Metronidazole is available for human use in the United States.

Note on Treatment in Pregnancy

Metronidazole is in pregnancy category B. Data on the use of metronidazole in pregnant women are conflicting. The available evidence suggests use during pregnancy has a low risk of congenital anomalies. Metronidazole may be used during pregnancy in those patients who will clearly benefit from the drug, although its use in the first trimester is generally not advised.

Pregnancy Category B: Either animal-reproduction studies have not demonstrated a fetal risk but there are no controlled studies in pregnant women or animal-reproduction studies have shown an adverse effect (other than a decrease in fertility) that was not confirmed in controlled studies in women in the first trimester (and there is no evidence of a risk in later trimesters).

Note on Treatment During Lactation

Metronidazole is excreted in breast milk. The American Academy of Pediatrics classifies metronidazole as a drug for which the effect on nursing infants is unknown but may be of concern. The World Health Organization (WHO) advises to avoid metronidazole treatment in lactating women. Metronidazole should be used during lactation only if the potential benefit of therapy to the mother justifies the potential risk to the infant.

Note on Treatment in Pediatric Patients

The safety of metronidazole in children has not been established. Metronidazole is listed as an antiamebic and antigiardiasis medicine on the WHO Model List of Essential Medicines for Children, intended for the use of children up to 12 years of age.

Trimethoprim–sulfamethoxazole

Trimethoprim–sulfamethoxazole (TMP–SMX) is available for human use in the United States.

Note on Treatment in Pregnancy

Trimethoprim–sulfamethoxazole (TMP–SMX) is in pregnancy category C. TMP–SMX should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. TMP-SMX should be avoided near-term because of the potential for hyperbilirubinemia and kernicterus in the newborn.

Pregnancy Category C: Either studies in animals have revealed adverse effects on the fetus (teratogenic or embryocidal, or other) and there are no controlled studies in women or studies in women and animals are not available. Drugs should be given only if the potential benefit justifies the potential risk to the fetus.

Note on Treatment During Lactation

Trimethoprim–sulfamethoxazole (TMP–SMX) is excreted in breast milk. TMP–SMX generally is compatible with breastfeeding of healthy, full-term infants after the newborn period. However, TMP-SMX generally should be avoided by women when nursing infants who are premature, jaundiced, ill, or stressed, or who have glucose-6-phosphate dehydrogenase deficiency.

Note on Treatment in Pediatric Patients

The safety of trimethoprim–sulfamethoxazole (TMP–SMX) in children has not been systematically evaluated. Use in children less than 2 months of age generally is not recommended.

Nitazoxanide

Nitazoxanide is available for human use in the United States.

Note on Treatment in Pregnancy

Nitazoxanide is in pregnancy category B. Data on the use of nitazoxanide in pregnant women are limited, and risk to the embryo-fetus is unknown. Nitazoxanide should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Pregnancy Category B: Either animal-reproduction studies have not demonstrated a fetal risk but there are no controlled studies in pregnant women or animal-reproduction studies have shown an adverse effect (other than a decrease in fertility) that was not confirmed in controlled studies in women in the first trimester (and there is no evidence of a risk in later trimesters).

Note on Treatment During Lactation

It is not known whether nitazoxanide is excreted in breast milk. Nitazoxanide should be used with caution in breastfeeding women.

Note on Treatment in Pediatric Patients

Nitazoxanide tablets should not be used in children age 11 years or younger as a single tablet contains a greater dose than recommended for pediatric dosing. Nitazoxanide oral suspension may be used for dosing in children, although the safety in children age 1 and younger is not certain.

Paromomycin (Oral)

Oral paromomycin is available for human use in the United States.

Note on Treatment in Pregnancy

Oral paromomycin has not been assigned to a pregnancy category by the Food and Drug Administration. Data on the use of oral paromomycin in pregnant women are limited, and the risk to the embryo-fetus probably is low. Oral paromomycin generally is poorly absorbed from the gastrointestinal tract, with minimal, if any, systemic availability.

Note on Treatment During Lactation

Oral paromomycin is unlikely to be excreted in breast milk, and the drug generally is poorly absorbed from the gastrointestinal tract.

Note on Treatment in Pediatric Patients

The safety of oral paromomycin in children has not been formally evaluated. However, the safety profiles likely are comparable in children and adults.

Iodoquinol

Iodoquinol is available for human use in the United States.

Note on Treatment in Pregnancy

Oral iodoquinol has not been assigned a pregnancy category by the Food and Drug Administration. Data on the use of iodoquinol in pregnant women are limited, and risk to the embryo-fetus is unknown. Iodoquinol should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Note on Treatment During Lactation

It is not known whether iodoquinol is excreted in breast milk. Iodoquinol should be used with caution in breastfeeding women.

Note on Treatment in Pediatric Patients

The safety of iodoquinol in children has not been established.

Ketoconazole

Ketoconazole is available for human use in the United States.

Note on Treatment in Pregnancy

Ketoconazole is in pregnancy category C. Data on the use of ketoconazole in pregnant women are limited, and the risk to the embryo-fetus is unknown. Ketoconazole should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Pregnancy Category C: Either studies in animals have revealed adverse effects on the fetus (teratogenic or embryocidal, or other) and there are no controlled studies in women or studies in women and animals are not available. Drugs should be given only if the potential benefit justifies the potential risk to the fetus.

Note on Treatment During Lactation

According to a case report, ketoconazole was excreted in breast milk and the nursing infant did not have adverse effects. The American Academy of Pediatrics classifies ketoconazole as compatible with breastfeeding.

Note on Treatment in Pediatric Patients

The safety of ketoconazole has not been evaluated systematically for children of any age, and essentially no data are available about its use in children less than 2 years of age. Ketoconazole should not be used in children unless the potential benefit outweighs the risks.

References

  • Stensvold CR, Smith HV, Nagel R, Olsen KE, Traub RJ. Eradication of Blastocystis carriage with antimicrobials: reality or delusion? J Clin Gastroenterol 2010;44:85-90.
  • Tan KS. New insights on classification, identification, and clinical relevance of Blastocystis spp. Clin Microbiol Rev 2008:639-65.
  • Rossignol JF, Kabil SM, Said M, Samir H, Younis AM. Effect of nitazoxanide in persistent diarrhea and enteritis associated with Blastocystis spp.. Clin Gastroenterol Hepatol 2005 Oct;3(10):987-91.
  • Diaz E, Mondragon J, Ramirez E, Bernal R. Epidemiology and control of intestinal parasites with nitazoxanide in children in Mexico. Am J Trop Med Hyg 2003;68:384-5.
  • Nigro L, Larocca L, Massarelli L, Patamia I, Minniti S, Palermo F, Cacopardo B. A placebo-controlled treatment trial of Blastocystis spp. infection with metronidazole. J Travel Med 2003;10:128-30.
 
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