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Darvon (Propoxyphene Hydrochloride) - Description and Clinical Pharmacology

 
 



PULVULES®
DARVON®
PROPOXYPHENE
HYDROCHLORIDE
CAPSULES, USP

CIV

Rx only

DESCRIPTION

Darvon® (Propoxyphene Hydrochloride, USP) is an odorless, white crystalline powder with a bitter taste. It is freely soluble in water. Chemically, it is (2 S,3 R)-(+)-4-(Dimethylamino)-3-methyl-1,2-diphenyl-2-butanol propionate (ester) hydrochloride, which can be represented by the accompanying structural formula. Its molecular weight is 375.94.

Each Pulvule contains 65 mg (172.9 μmol) propoxyphene hydrochloride. It also contains D & C Red No. 33, F D & C Yellow No. 6, gelatin, magnesium stearate, silicone, starch, titanium dioxide, and other inactive ingredients.

CLINICAL PHARMACOLOGY

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 2 1/2 hours. After a 65-mg oral dose of propoxyphene hydrochloride, peak plasma levels of 0.05 to 0.1 μg/mL are achieved.

Repeated doses of propoxyphene at 6-hour intervals lead to increasing plasma concentrations, with a plateau after the ninth dose at 48 hours.

Propoxyphene is metabolized in the liver to yield norpropoxyphene. Propoxyphene has a half-life of 6 to 12 hours, whereas that of norpropoxyphene is 30 to 36 hours.

Norpropoxyphene has substantially less central-nervous-system-depressant effect than propoxyphene but a greater local anesthetic effect, which is similar to that of amitriptyline and antiarrhythmic agents, such as lidocaine and quinidine.

In animal studies in which propoxyphene and norpropoxyphene were continuously infused in large amounts, intracardiac conduction time (PR and QRS intervals) was prolonged. Any intracardiac conduction delay attributable to high concentrations of norpropoxyphene may be of relatively long duration.

ACTIONS

Propoxyphene is a mild narcotic analgesic structurally related to methadone. The potency of propoxyphene hydrochloride is from two thirds to equal that of codeine.

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