That is not able to be absorbed; not absorbable(adjective)
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Use "nonabsorbable" in a sentence
"About 40 percent of the patients who took rifaximin, a nonabsorbable antibiotic that stays in the gut, showed sustained relief during the two weeks they took the drug and during the 10-week follow-up period."
""Potential generic competitors would find it challenging to demonstrate bioequivalence to a nonabsorbable drug," he says."
"More than 1,200 patients participated in the Phase III, double-blind, multi-center studies of rifaximin, a nonabsorbable antibiotic that stays in the gut and is currently FDA-approved to treat traveler's diarrhea and hepatic encephalopathy."