PROPOXYPHENE NAPSYLATE and ACETAMINOPHEN TABLETS, USP
100 mg/650 mg
Propoxyphene napsylate, USP is an odorless, white crystalline solid with a bitter taste. It is very slightly soluble in water and soluble in methanol, ethanol, chloroform, and acetone. Chemically, it is (α S,1 R)-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 565.72.
C22H29NO2 • C10H8O3S • H2O
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 propoxyphene napsylate and acetaminophen contains 100 mg (176.8 µmol) propoxyphene napsylate and 650 mg (4,300 µmol) of acetaminophen and the following inactive ingredients: hypromellose, microcrystalline cellulose, magnesium stearate, polyethylene glycol, polysorbate 80, povidone, sodium lauryl sulfate, sodium starch glycolate, titanium dioxide, and D&C Red #30 aluminum lake.
Propoxyphene is a centrally acting narcotic analgesic agent. Equimolar doses of propoxyphene hydrochloride or napsylate provide similar plasma concentrations. Following administration of 65, 130, or 195 mg of propoxyphene hydrochloride, the bioavailability of propoxyphene is equivalent to that of 100, 200, or 300 mg respectively of propoxyphene napsylate. Peak plasma concentrations of propoxyphene are reached in 2 to 2½ hours. After a 100 mg oral dose of propoxyphene napsylate, peak plasma levels of 0.05 to 0.1 mcg/mL are achieved. As shown in Figure 1, the napsylate salt tends to be absorbed more slowly than the hydrochloride. At or near therapeutic doses, this absorption difference is small when compared with that among subjects and among doses.