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ENTEREG Capsules contain alvimopan, a peripherally-acting µ-opioid receptor (PAM-OR) antagonist. Chemically, alvimopan is the single stereoisomer [[2(S)-[[4(R)-(3-hydroxyphenyl)-3(R),4-dimethyl-1-piperidinyl]methyl]-1-oxo-3-phenylpropyl]amino]acetic acid dihydrate. It has the following structural formula:

Alvimopan is a white to light beige powder with a molecular weight of 460.6, and the empirical formula is C₂₅H₃₂N₂O₄•2H₂O. It has a solubility of < 0.1 mg/mL in water or buffered solutions between pH 3.0 and 9.0, 1 to 5 mg/mL in buffered solutions at pH 1.2, and 10 to 25 mg/mL in aqueous 0.1 N sodium hydroxide. At physiological pH, alvimopan is zwitterionic, a property that contributes to its low solubility.

ENTEREG Capsules for oral administration contain 12 mg of alvimopan on an anhydrous basis suspended in the inactive ingredient polyethylene glycol.

Last reviewed on RxList: 12/3/2009
This monograph has been modified to include the generic and brand name in many instances.