Propoxyphene Napsylate, USP is an odorless, white crystalline powder with a bitter taste. It is very slightly soluble in water and soluble in methanol, ethanol, chloroform, and acetone. Chemically, it is (αS,1R)-α-[2-(Dimethylamino)-1-methylethyl]-α-phenylphenethyl propionate compound with 2-naphthalenesulfonic acid (1:1) monohydrate, which can be represented by the accompanying structural formula. Its molecular weight is 565.74.

Propoxyphene napsylate differs from propoxyphene hydrochloride in that it allows more stable liquid dosage forms and tablet formulations. Because of differences in molecular weight, a dose of 100 mg (176.8 µmol) of propoxyphene napsylate is required to supply an amount of propoxyphene equivalent to that present in 65 mg (172.9 µmol) of propoxyphene hydrochloride.

Each tablet of Darvocet-N®50 contains 50 mg (88.4 µmol) propoxyphene napsylate and 325 mg (2,150 µmol) acetaminophen.

Each tablet of Darvocet-N®100 contains 100 mg (176.8 µmol) propoxyphene napsylate and 650 mg (4,300 µmol) acetaminophen.

Each tablet also contains amberlite, cellulose, F D & C Yellow No. 6, magnesium stearate, stearic acid, titanium dioxide, and other inactive ingredients.

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