pentazocine hydrochloride
Talwin, Talwin Nx (with naloxone hydrochloride)

pentazocine lactate
Talwin

Available forms
Available by prescription only
Injection: 30 mg/ml
Tablets: 50 mg

Indications and dosages
 Moderate to severe pain. Adults: 50 to 100 mg P.O. q 3 to 4 hours, p.r.n., or around the clock. Maximum oral dose is 600 mg daily. Or 30 mg I.M., I.V., or S.C. q 3 to 4 hours, p.r.n., or around the clock. Maximum parenteral dose is 360 mg daily. Doses above 30 mg I.V. or 60 mg I.M. or S.C. not recommended.  For patients in labor, give 30 mg I.M. or 20 mg I.V. in 2- to 3-hour intervals.

Pharmacodynamics
Analgesic action: Exact mechanism unknown. Believed to be a competitive antagonist at some receptors and an agonist at others, resulting in relief of moderate pain.
 Can produce respiratory depression, sedation, miosis, and antitussive effects. Also may cause psychotomimetic and dysphoric effects. In patients with coronary artery disease, drug elevates mean aortic pressure, left ventricular end-diastolic pressure, and mean pulmonary artery pressure. In patients with acute MI, I.V. drug increases systemic and pulmonary arterial pressures and systemic vascular resistance.

Pharmacokinetics
Absorption: Well absorbed after oral or parenteral administration. However, orally administered drug undergoes first-pass metabolism in liver; less than 20% of dose reaches systemic circulation unchanged. Increased bioavailability in patients with hepatic dysfunction; patients with cirrhosis absorb 60% to 70% of drug.
Distribution: Widely distributed in body.
Metabolism: Metabolized in liver, mainly by oxidation and secondarily by glucuronidation. Metabolism may be prolonged in patients with impaired hepatic function.
Excretion: Duration of effect is 3 hours. Considerable variability among patients in its urinary excretion. Small amounts excreted in feces after oral or parenteral administration.

Contraindications and precautions
Contraindicated in patients hypersensitive to drug or its components and in children younger than age 12. Use cautiously in patients with impaired renal or hepatic function, acute MI, head injury, increased intracranial pressure, or respiratory depression.

Interactions
Drug-drug. Barbiturates (such as thiopental): If administered within a few hours of these drugs, pentazocine may produce additive CNS and respiratory depressant effects; may cause apnea. Separate administration times if used together.
Cimetidine: Increases pentazocine toxicity; causes disorientation, respiratory depression, apnea, and seizures. Monitor patient; be prepared to give naloxone if toxicity occurs.
CNS depressants (antihistamines, barbiturates, benzodiazepines, muscle relaxants, narcotic analgesics, phenothiazines, sedative-hypnotics, tricyclic antidepressants): Potentiates respiratory and CNS depression, sedation, and hypotensive effects. Reduced doses of pentazocine usually are needed.
Drugs extensively metabolized in liver (digitoxin, phenytoin, rifampin): Causes drug accumulation and enhanced effects. Monitor patient for toxicity.
General anesthetics: May cause severe CV depression. Avoid use together.
Narcotic agonist-antagonist, single dose of an antagonist: Patients who become physically dependent on pentazocine may experience acute withdrawal syndrome. Use cautiously; monitor patient closely.
Drug-lifestyle. Alcohol use: Potentiates respiratory and CNS depression, sedation, and hypotensive effects. Discourage alcohol use.

Adverse reactions
CNS: sedation, visual disturbances, hallucinations, drowsiness, dizziness, light-headedness, confusion, euphoria, headache, syncope, psychotomimetic effects.
CV: circulatory depression, shock, hypertension, hypotension.
EENT: blurred vision, nystagmus.
GI: dry mouth, nausea, vomiting, constipation, taste alteration.
GU: urine retention.
Hematologic: WBC depression.
Respiratory: respiratory depression, dyspnea, apnea.
Skin: induration, nodules, sloughing, and sclerosis of injection site; diaphoresis; pruritus.
Other: hypersensitivity reactions (anaphylaxis), physical and psychological dependence.

Effects on lab test results
None reported.

Overdose and treatment
The signs and symptoms of overdose haven’t been defined because of lack of clinical experience with overdose.
 If overdose occurs, use supportive measures (including oxygen, I.V. fluids, vasopressors) as needed. Consider mechanical ventilation. Parenteral naloxone is an effective antagonist for respiratory depression because of pentazocine.

Special considerations
• Tablets aren’t well absorbed.
• For I.V. administration, inject undiluted by slow I.V. bolus. Don’t exceed a 30-mg dose.
• Don’t mix in same syringe with soluble barbiturates.
• Pentazocine may obscure signs and symptoms of an acute abdominal condition or worsen gallbladder pain.
• Drug possesses narcotic antagonist properties. May precipitate abstinence syndrome in narcotic-dependent patients.
• Talwin-Nx, the available oral pentazocine, contains the narcotic antagonist naloxone, which prevents illicit I.V. use.
• Use S.C. route only when needed. Severe tissue damage is possible at injection site.
• Drug may cause orthostatic hypotension in ambulatory patients. Have patient sit down to relieve symptoms.
Breast-feeding patients
• It isn’t known if drug appears in breast milk. Use cautiously in breast-feeding women.
Pediatric patients
• Drug isn’t recommended for children younger than age 12.
Geriatric patients
• Lower doses are usually indicated for elderly patients, who may be more sensitive to therapeutic and adverse effects of drug.

Patient education
• Tell patient to report rash, confusion, disorientation, or other serious adverse effects.
• Warn patient that Talwin-Nx is for oral use only. Severe reactions may result if tablets are crushed, dissolved, and injected.
• Tell patient to avoid use of alcohol and other CNS depressants.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use