Treatment of Albendazole-Resistant Roundworm Infection
For roundworm (Ascaris lumbricoides) infection that has failed albendazole treatment, switch to mebendazole 100 mg twice daily for 3 days or consider ivermectin 200 μg/kg as a single dose. 1
Primary Alternative: Mebendazole
- Mebendazole is the first-line alternative for albendazole-resistant Ascaris infection, with FDA-approved efficacy showing a 98% cure rate for common roundworm. 1
- The recommended regimen is mebendazole 100 mg orally twice daily for 3 days, which provides superior efficacy compared to single-dose treatment. 1
- Mebendazole achieves a 99% egg reduction rate in Ascaris infections, making it highly effective even in treatment-resistant cases. 1
Secondary Alternative: Ivermectin
- Ivermectin 200 μg/kg as a single oral dose is highly effective against Ascaris, with cure rates of 83-100% in clinical trials. 2, 3
- Ivermectin provides the advantage of single-dose administration, improving compliance compared to multi-day regimens. 2
- However, ivermectin is ineffective against hookworms and has limited efficacy against whipworm (only 11% cure rate for Trichuris), so it should only be used if roundworm is the sole confirmed infection. 2
Important Clinical Considerations
Confirming True Resistance vs. Reinfection
- Treatment failure is rare with albendazole for Ascaris (standard cure rate 98%), so persistent infection more commonly indicates reinfection rather than true drug resistance. 4, 5
- Repeat stool examination 2-3 weeks after treatment to distinguish between treatment failure and new infection. 6
- Consider environmental factors: ongoing exposure through contaminated soil, unwashed produce, or poor sanitation increases reinfection risk. 6
Dosing Specifics
- For mebendazole: 100 mg twice daily for 3 days is the standard regimen for all ages. 1
- For ivermectin: 200 μg/kg single dose (approximately 12 mg for a 60 kg adult, 6 mg for a 30 kg child). 4
- Some guidelines accept ivermectin 150 μg/kg as an alternative dose, though 200 μg/kg is preferred. 4, 3
Safety Monitoring
- Monitor for hepatotoxicity and leukopenia if treatment extends beyond 14 days, particularly relevant if multiple courses are needed. 6, 7
- Both mebendazole and ivermectin are generally well-tolerated with minimal side effects. 2, 3
Mixed Infections
- If mixed helminth infection is suspected (roundworm plus hookworm or whipworm), mebendazole is preferred over ivermectin due to broader spectrum activity. 1, 2
- Mebendazole is effective against pinworm, whipworm, roundworm, and hookworm in single or mixed infections. 1
Common Pitfalls to Avoid
- Do not assume drug resistance without confirming adequate initial dosing: standard albendazole dose for Ascaris is 400 mg as a single dose, with repeat in 2 weeks. 4
- Do not use ivermectin in patients with potential Loa loa co-infection (those who have traveled to endemic regions in Central/West Africa) without first excluding loiasis, as this can cause severe encephalitis. 4
- Ensure proper stool collection technique: multiple stool samples on different days may be needed due to intermittent egg shedding. 6