Reese's pinworm medicine is available in US at any pharmacy and it works well, no prescription required, also available online.
Ivermectin works well too. can buy on Amazon as Ivomec injectable. it can be taken orally, rectally, or topically. The dosing is by weight on the box, and online. The CDC published a note saying the vet version of Ivermenctin (Ivomec) is approved for human use when patients cant tolerate oral tablets. It even says can be used rectally.
I have used Ivomec by putting the liquid into an empty capsule and taking orally.