Is it safe to take vermox once a week?

Yes: Vermox is a relatively safe drug for intestinal worms and parasites the usual dose is not once a week. The dose is one 100 mg pill twice a day for 3 days

Likely safe: We use much higher doses for a long period to treat some conditions. However, I would wonder why it would be needed. An adult rarely gets pin worms, which is one of the few things this dose would treat. They also rarely get re-infected. However, some assume that an itchy bottom must be due to this agent, while there are many other possibilities.