Give it a few hours and try again
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The poop has to be moved down quite low for a suppository to have an effect...
Did you manage to keep it in him for at least 20 mins? It can be tough, but it can take that long to work when they are horribly backed up...
Have they ever done an enema on him to get things cleared out quickly? That's what the dr did with Alexandra the first trip to the ER.. a Fleet enema (you can get them at the drugstore, just use half of the liquid) and then three consecutive days of glycerin suppositories to get her all sparkly on the inside
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