While reviewing the literature out of concern for my own present problems, I came across the following study which found differences in cure rates for different brands of mebendazole. Out of three brands, only Vermox by Janssen showed high cure rate for trichuriasis. A notable difference wasn't found for ascariasis, but that might simply be due to the fact that Ascaris lumbricoides doesn't require a particularly potent dose.

So, when purchasing mebendazole, it might be best to choose Vermox (Janssen). Also, while reviewing the literature I found multiple studies concluding that single doses of mebendazole, even high dosages, don't work well to treat certain infections. So it's always best to do the three-day dosing as opposed to a single dose even though some references still point to single dosing as an option.

(study below).

East Afr Med J. 2004 Mar;81(3):134-8.

Comparative efficacy of albendazole and three brands of mebendazole in the treatment of ascariasis and trichuriasis.

Legesse M, Erko B, Medhin G.
Source

Institute of Pathobiology, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia.

OBJECTIVE:
To evaluate the comparative efficacy of 400 mg albendazole (Smith Kline Beecham) as a single dose and three brands of mebendazole (Janssen, Unibios and East African Pharmaceuticals) at doses of 100 mg twice a day for three consecutive days in the treatment of single or mixed infections with Ascaris lumbricoides and or Trichuris trichiura in four treatment groups of school children.

DESIGN:
Randomized trial.

SETTING:
Wondo-Genet, southern Ethiopia. Subjects: School children, aged six to nineteen years.

RESULTS:
The percentage cure rate and egg reduction rate obtained with albendazole and mebendazole from the three brands were not significantly different in the treatment of ascariasis. However, significant differences were found among the percentage cure rates and egg reduction rates of the four treatment groups in the treatment of trichuriasis. Comparatively, high cure rate (89.8%) and egg reduction rate (99.1%) were observed in vermox (Janssen) treated group followed by Unibios (India) treated group (53.3% and 96.53% cure and egg reduction rates, respectively), whereas low cure rate (17.1%) and egg reduction rate (69.8%) were seen in the albendazole treated group.

CONCLUSION:
The results of this study suggest that in areas of single or mixed infections with Trichuris trichiura and/or Ascaris lumbricoides are common public health problems and where laboratory facilities are not available to make parasite identification, mebendazole (particularly vermox, a product of Janssen laboratory) would be the drug of choice to treat trichuriasis and ascariasis. However, either mebendazole from the different brands or albendazole is effective in the treatment of ascariasis in areas where trichuriasis is not prevalent.