Most products I have found err on the side of conservatism, in terms of their recommended dosage. My experience is that I have to be very aggressive with my cleansing protocol in order to diminish the colonies a little. It took almost a year of cleansing continuously, for me to stop being afraid that I was about to die from the infection.
A rule of thumb is that you must cleanse your body one month for every year you've suffered from a chronic infection. I got my first case of pinworms when I was a little kid. I'm 51. I plan to get rid of them by cleansing persistently for 4-5 years.
You cannot expect to get rid of them by taking one round of medicine. They lay eggs that hatch out. There is an opportunity for reinfection from the water we drink, the air we breathe, the food we eat, and the people we hug.
You have to go after them repeatedly. You have to be persistent, tenacious and aggressive. At least that has been my experience.