There are pretty much three things you have to do when dealing with parasites. So far you only mentioned doing one, giving the medication.
As already mention, you have to keep the cage clean. Re-contamination is very easy to happen, could simply be a cricket running over the dragon's poop or the spot the poop was, and then getting eaten by the dragon. Strip the cage down and give it a complete and throughout cleaning. If the cage is glass or plastic, soak it in a bleach solution (I would actually use a stronger concentration than recommended, a one part bleach to 10 parts water) after washing the cage with soap and rinsing. Soak in this solution for 20 minutes, then rinse the cage and all furnature many times with cold clean water till you can no longer smell bleach on it. Set out in a well vented area (or outside) to dry.
Any furnature that is wooden or porous, toss out if at all possible. If it can't be thrown out, bake in the oven at about 240F for several hours. Cool. Make sure any wood is already very dry before baking, as greenish wood can split when baked, or ooze sap all over your oven.
If the cage itself is wooden and not sealed.....toss it. If impractical, put the cage through the bleech treatment but leave ouside for a good 24 hours then seal it with urathane or other wood sealing finish. Let dry completely for another 24 hours after the final coat.
Assuming you can put the dragon back into it's original cage (if not, then use a temporary cage, even if small, just make sure it's at least twice the length of the dragon and that length wide. A rubbermaid container can be used in a pinch). Keep the cage as barebones as possible, basking spot, lamp, UVB bulb, hide is all the cage needs. Line it with papertowel or newspaper.
During the entire treatment and every bowel movement, remove all the paper, not just the soiled area, disinfect the floor of the cage, put in new papertowel/newsprint. Keep this up for a good week after the treatment end, to ensure the parasites are gone.
ALso, during the treatment and for a couple weeks afterwards, give your dragon a probiotic. This can be acidophyllis, pediatric (the probiotic given to kids) and even just regular unsweetened low fat yogurt that contains an active bacteria culture. (a teaspoon a day is good).
Giving the dragon itself a bath is a good ideal too, especially at the start of his treatment and anytime you suspect he ran through his poop before you cleaned it up.
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PHLdyPayne