Treatment of Blastocystis hominis Infection
Metronidazole is the recommended first-line treatment for symptomatic Blastocystis hominis infections, with a typical dosage of 500-750 mg three times daily for 10 days. However, treatment efficacy is variable and should be reserved for patients with persistent symptoms after excluding other causes.
When to Treat
Treatment for B. hominis should be considered in these scenarios:
- Persistent gastrointestinal symptoms (abdominal pain, diarrhea, nausea, flatulence)
- No other identifiable cause for symptoms
- Confirmed presence of B. hominis in stool samples
- Immunocompromised patients with symptoms
First-Line Treatment Options
Metronidazole:
- Dosage: 500-750 mg three times daily for 10 days 1
- Efficacy: Variable (33-80% eradication rates reported)
- Patients should avoid alcohol during treatment and for 24 hours afterward
Alternative options if metronidazole fails or is contraindicated:
- Trimethoprim/Sulfamethoxazole (TMP/SMX): 1 tablet three times daily for 10 days 1
- Efficacy: Lower than metronidazole (approximately 22% eradication)
Special Populations
Pregnant Women
- Metronidazole should be avoided in the first trimester 2
- For symptomatic cases requiring treatment in later trimesters, consult with specialists as the CDC states oral metronidazole is generally safe after the first trimester 2
Children
- Metronidazole: 30 mg/kg twice daily for 10 days 3
- Saccharomyces boulardii: 250 mg twice daily for 10 days (alternative option with similar efficacy) 3
Treatment Efficacy and Follow-up
Research shows variable efficacy of standard treatments:
- Clinical cure rates with metronidazole range from 66-80% 3, 4
- Microbiological cure rates are often lower (48-80%) 3, 4
- There appears to be a relationship between clinical and microbiological response 4
If first-line treatment fails:
- Consider a second course with an alternative agent
- Re-evaluate for other potential causes of symptoms
- Consider combination therapy in resistant cases
Monitoring Response
- Follow-up stool examination 15-30 days after treatment completion
- If symptoms persist and B. hominis is still present, consider alternative treatment
- Second-line treatments have shown approximately 70% efficacy in patients who failed initial therapy 4
Prevention
Since B. hominis is transmitted via the fecal-oral route, prevention focuses on:
- Proper hand hygiene
- Food and water precautions, especially when traveling
- Safe food handling practices
Important Considerations
- The pathogenicity of B. hominis remains controversial 5, 6
- Treatment should be limited to patients with persistent symptoms and after a complete workup for alternative etiologies 3
- Always search for potential co-pathogens in symptomatic patients 5
- Treatment failures are common, and multiple courses may be necessary in persistent cases
Despite ongoing debates about its pathogenicity, symptomatic patients with confirmed B. hominis infection and no other identified cause for their symptoms may benefit from treatment with metronidazole as the first-line option.