Take the dragon to the vet and explain that you have already run a home test and it came out positive for giardia and ask for the treatment. I cant remember off the top of my head which antibiotic/dewormer they use for it. I wouldnt advise trying to dose the medications at home...if you get the suspensions or the dosage wrong it could be really devastating to your beardie.
Just out of curiosity, how did you preform the test at home? do you have a snap test or was it just by floatation and microscope i.d?
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0.1 Bearded dragon
0.1 mexican Black kingsnake
1.1.2 Leopard Gecko's (normal:normal:tang:baldy hypo tang)
0.0.1 Tokay Gecko
1.0 Blue Tongue Skink
0.0.1 Reverse Okeetee Corn
0.1 Anerythristic Corn
0.0.1 Red Tegu
0.1 Bullmastiff
4.1 Cats