Darvon 642 , Novopropoxyn 
Classifications: narcotic (opiate) agonist, analgesic;
Therapeutic: narcotic analgesic, agonist

Prototype: Morphine
Pregnancy Category: C (D for prolonged use or at term)
Controlled Substance: Schedule IV


Napsylate: 100 mg tablets

Hydrochloride: 65 mg capsules


Centrally acting opioid structurally related to methadone. Acts as a weak agonist at opiate receptors within the CNS. Analgesic potency about ? –2/3 that of codeine.

Therapeutic Effect

Potent analgesic.


Relief of mild to moderate pain.

Unlabeled Uses

To suppress narcotic withdrawal symptoms.


Hypersensitivity to drug; suicidal individuals; alcoholism; dependence on opiates; safety during pregnancy [category C (D for prolonged use or at term)] or in children is not established.

Cautious Use

Kidney or liver disease; cardiac disease; biliary tract disease; pulmonary insufficiency.

Route & Dosage

Mild to Moderate Pain
Adult: PO 65 mg HCl or 100 mg napsylate q4h prn (max: 390 mg HCl/d, 600 mg napsylate/d)


Note: 100 mg napsylate = 65 mg HCl

  • Empty capsules and mix contents with water or food if unable to swallow capsule whole.
  • Be aware that absorption may be delayed by presence of food in stomach.
  • Store at 15°–30° C (59°–86° F).

Adverse Effects (≥1%)

CNS: Dizziness, light-headedness, drowsiness, sedation, unusual fatigue or weakness, restlessness, tremor, euphoria, dysphoria, headache, paradoxic excitement, mental confusion, toxic psychosis, coma, convulsions. GI: Nausea, vomiting, abdominal pain, constipation, liver dysfunction. Special Senses: Minor visual disturbances, pinpoint pupils (dilate with advancing hypoxia). Skin: Skin eruptions (hypersensitivity). Metabolic: Hypoglycemia (patients with impaired kidney function), acidosis, nephrogenic diabetes insipidus. Respiratory: Respiratory depression, pulmonary edema. CV: Circulatory collapse, ECG abnormalities.


Drug: Alcohol and other cns depressants add to CNS depression, also fatalities reported with alcohol use; may increase hypoprothrombinemic effects of warfarin; may increase carbamazepine toxicity through decreased metabolism; orphenadrine increases CNS stimulation, anxiety, tremors, confusion. Herbal: St. John's wort may increase sedation.


Absorption: Readily from upper part of small intestine. Onset: 15–60 min. Peak: 2–3 h. Duration: 4–6 h. Distribution: Crosses placenta; distributed into breast milk. Metabolism: In liver. Elimination: In urine. Half-Life: 6–12 h, 30–36 h for metabolite.

Nursing Implications

Assessment & Drug Effects

  • Evaluate need for drug since abuse potential is high.
  • Monitor CNS effects, respiratory status and therapeutic effectiveness.
  • Overdose: Prompt action required; fatalities occur commonly within first hour following overdosage.

Patient & Family Education

  • Do not drive or engage in potentially hazardous activities until response to drug is known.
  • Do not exceed recommended dose; do not use alcohol and other CNS depressants with propoxyphene.
  • Lie down if dizziness, light-headedness, drowsiness, nausea, or vomiting occur while ambulating.
  • Be aware that tolerance and physical or psychic dependence of the morphine type can occur with excessive use.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

© 2006-2022 Last Updated On: 12/03/2022 (0)
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