The treatment suggested points towards a mite infestation
of skin known as scabies
.It can occur in anyone. I would advise you to follow your doctor's prescription as the treatment must have been suggested after proper skin examination. With single application of permethrin, you will see a noticeable reduction in itching. However complete recovery from itching might take two to three weeks and for the same, your doctor advised you to continue the medicines for the said period. Hope that solves your query. Take care.