naloxone/pentazocine (Talwin NX)

Introduction

50 mg pentazocine + 0.5 mg naloxone. DEA-controlled substance: class 4.

Indications

• treatment of mild to moderate acute pain-related syndromes
• treatment of some chronic pain syndrome

Contraindications

• increase intracranial pressure (unless patient is mechanically ventilated)

Caution:

• NOT recommended for patients with seizures or psychosis

Dosage

• 1 tab PO every 3-4 hours or every 4-6 hours; max: 12 tabs/day
• 1 tab every 6-8 hours with hepatic dysfunction; max: 8 tabs/day

Pharmacokinetics

• well absorbed orally
• only 20% reaches circulation unchanged due to 1st pass metabolism
• bioavailability is increased in patients with hepatic dysfunction
• onset of analgesia is 15-30 minutes
• duration of action is 3-4 hours
• metabolized in liver
• elimination 1/2life is 2-3 hours, prolonged with hepatic dysfunction

Adverse effects

• common (> 10%)
  • euphoria, nausea/vomiting, weakness, drowsiness
• less common (1-10%)
  • malaise, headache, hypotension, restlessness, nightmares, ureteral spasm, dry mouth, blurred vision, rash, dyspnea
• uncommon (< 1%)
  • GI irritation, insomnia, palpitations, bradycardia, peripheral vasodilation, CNS depression, sedation, hallucinations, confusion, disorientation, seizures may occur in seizure-prone patients, pruritus, antidiuretic hormone release, constipation, tissue injury with IM & SC administration, miosis, biliary spasm, histamine release, increased intracranial pressure, physical & psychologic dependence
• other
  • respiratory depression
  • constipation (generally mild)
  • withdrawal in opiate-dependent patients
• overdose:
  • airway support
  • IV administration of naloxone
    • 2 mg (0.01 mg/kg in children)
    • may repeat up to a total of 10 mg

Drug interactions

• opioid agonists: mu receptor antagonism may precipitate withdrawal
• naloxone is a direct opioid antagonist
• fluoxetine in combination may cause serotonin syndrome
• MAO inhibitors in combination may result in hypertensive crisis
• additive effects with other CNS depressants
  • phenothiazines
  • sedatives
  • anxiolytics
  • hypnotics
  • alcohol
• tripepennamine potentiates pentazocine effects & toxicity

Mechanism of action

• opioid partial agonist
  • competitive antagonist at opioid mu receptors
  • agonist at opioid kappa & sigma receptors
  • will stimulate withdrawal in physically-dependent patients
• naloxone
  • given orally has no effect on activity of pentazocine
  • if ground & given parenterally, naloxone will antagonize effects of pentozocine
  • added to prevent abuse by injecting ground & dissolved tablets

More general terms

• pharmacologic combination

Components

• naloxone (Narcan, Evzio, ReVive)
• pentazocine (Talwin)