Key points
- The clinical significance of Blastocystis spp. is controversial.
- Several different medications have been used to treat Blastocystis with varying degrees of success.
- Consider safety precautions of medications in different populations.
Treatment options
Treatment with metronidazole* at various doses has been reported, for example (adults):
Drug
Example adult dosage
Duration
Metronidazole
250 mg – 750 mg, orally
3x/day for 10 days
Metronidazole
1500 mg, 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 in adults:
Drug
Example adult dosage
Duration
Trimethoprim(TMP) */
sulfamethoxazole (SMX)*
6 mg/kg TMP*, 30 mg/kg SMX*
Once daily for 7 days
Trimethoprim(TMP) */
sulfamethoxazole (SMX)*
320mg TMP*, 1600 mg SMX*
Once daily for 7 days
Trimethoprim(TMP) */
sulfamethoxazole (SMX)*
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:
Drug
Example dosage
Duration
Nitazoxanide*
Adults: 500 mg, orally
Twice daily for 3 days
Nitazoxanide*
Children 4 – 11 years: 200 mg, orally
Twice daily for 3 days
Nitazoxanide*
Children 1 – 3 years: 100 mg, orally
Twice daily for 3 days
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.
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.
Care precautions
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 should be weighed against any potential risks.
Pregnancy Category B: Either animal-reproduction studies have not demonstrated a fetal risk but there are no adequate and well-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 adequate and well-controlled studies in women in the first trimester (and there is no evidence of a risk in later trimesters).
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.
Treatment in Pediatric Patients
The safety of metronidazole in children has not been established. Metronidazole is listed for the treatment of complicated intra-abdominal infections on the WHO Model List of Essential Medicines for Children, intended for the use of children up to 12 years of age.
Treatment in Pregnancy
Trimethoprim–sulfamethoxazole (TMP–SMX) is a pregnancy category C drug. 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 adequate and well-controlled studies in pregnant women or adequate and well-controlled studies in pregnant women and animals are not available. Drugs should be given only if the potential benefit justifies the potential risk to the fetus.
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.
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.
Treatment in Pregnancy
Nitazoxanide is a pregnancy category B drug. Data on the use of nitazoxanide in pregnant women are limited, and risk to the embryo-fetus is unknown. Healthcare providers should consider the risk of treatment in infected pregnant women with the potential risk to the fetus in the absence of treatment.
Pregnancy Category B: Either animal-reproduction studies have not demonstrated a fetal risk but there are no adequate and well-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 adequate and well-controlled studies in women in the first trimester (and there is no evidence of a risk in later trimesters).
Treatment during lactation
Nitazoxanide is excreted in breast milk. Available evidence is inconclusive or inadequate for determining infant risk when used during breastfeeding. Nitazoxanide should be used with caution in breastfeeding women.
Treatment in pediatric patients
Nitazoxanide tablets should not be used in children aged 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 aged 1 and younger is not certain.