question: My 4 year old son woke on Thursday night with terrible itching in his bottom. He's had threadworm before and as the symptoms were the same I assumed it was threadworm again (despite not seeing any worms or eggs). He had a dose of Ovex on Thursday night but woke up again last night at the same time with itching again. How long does it take for the Ovex to work usually? Should I give him another dose?