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 (aS,1R)-a-[2-(Dimethylamino)-1-methylethyl]-a-phenylphenethyl propionate compound with 2-naphthalenesulfonic acid (1:1) monohydrate. Its molecular weight is 565.72.
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 mcmol) of propoxyphene napsylate is required to supply an amount of propoxyphene equivalent to that present in 65 mg (172.9 mcmol) of propoxyphene hydrochloride.
Each Darvocet-N 50 tablet contains 50 mg (88.4 mcmol) propoxyphene napsylate and 325 mg (2,150 mcmol) acetaminophen.
Each Darvocet-N 100 tablet contains 100 mg (176.8 mcmol) propoxyphene napsylate and 650 mg (4,300 mcmol) acetaminophen.
Each tablet also contains amberlite, cellulose, FD&C Yellow #6, magnesium stearate, stearic acid, titanium dioxide, and other inactive ingredients.