Adult: Initially, 50 mg 3-4 hourly. Usual dose: 25-100 mg 3-4 hourly. Max: 600 mg daily. Dosage is individualised based on the pain severity, patient response, and concomitant medications. Child: 6-12 years 25 mg 3-4 hourly as necessary. Dosage is individualised based on the pain severity, patient response, and concomitant medications.
Renal Impairment
Severe: Dose reduction may be necessary.
Hepatic Impairment
Severe: Dose reduction may be necessary.
Administration
Pentazocine Should be taken with food.
Contraindications
Significant respiratory depression (particularly in the presence of cyanosis and excessive bronchial secretion); acute alcoholism; raised intracranial pressure, head injury, or pathological brain conditions where clouding of the sensorium is undesirable; acute bronchial asthma; heart failure secondary to chronic lung disease; porphyria. Concomitant use or within 14 days after MAOI therapy.
Special Precautions
Patient with acute MI or other clinical situations where alterations of vascular resistance and blood pressure are undesirable or may not be tolerated; current or history of substance abuse disorder (including alcohol misuse) or mental health conditions (e.g. depression, anxiety disorders, PTSD); history of or risk factors for seizure disorders; sleep-related disorders (e.g. sleep apnoea); inflammatory or obstructive bowel disorders, cholecystitis, pancreatitis or other abdominal conditions; respiratory disease; adrenal insufficiency (e.g. Addison's disease), prostatic hypertrophy, phaeochromocytoma, hypothyroidism. Avoid abrupt withdrawal. Severe hepatic and renal impairment. Elderly. Pregnancy and lactation.
Adverse Reactions
Significant: May increase systemic and pulmonary arterial pressure and systemic vascular resistance; CNS depression; secondary hypogonadism (long-term use) which may progress to mood disorders and osteoporosis, sphincter of Oddi constriction, seizures, central sleep apnoea (dose-dependent), opioid drug withdrawal syndrome, hyperalgesia (long-term use). Blood and lymphatic system disorders: Eosinophilia, agranulocytosis. Cardiac disorders: Tachycardia, bradycardia, palpitations. Gastrointestinal disorders: Constipation, dry mouth, nausea, vomiting. General disorders and administration site conditions: Face oedema, chills, hypothermia. Immune system disorders: Allergic reactions. Investigations: WBC decreased. Nervous system disorders: Headache, dizziness, paraesthesia, tremors, sedation. Psychiatric disorders: Euphoria, floating feeling, depression, mood altered, disorientation, confusion, insomnia, nightmares. Renal and urinary disorders: Urinary retention, ureteral spasm. Reproductive system and breast disorders: Decreased libido. Respiratory, thoracic and mediastinal disorders: Dyspnoea. Skin and subcutaneous tissue disorders: Rash, urticaria, dermatitis, pruritus, diaphoresis, toxic epidermal necrolysis. Vascular disorders: Hypertension, hypotension, flushing, syncope, circulatory depression. Potentially Fatal: Respiratory depression; opioid abuse, overuse or misuse.
This drug may cause drowsiness, dizziness, and impair physical or mental abilities, if affected, do not drive or operate machinery.
Monitoring Parameters
Monitor for blood pressure, bowel function, respiratory and mental status, and pain relief. Evaluate each patient's risk for opioid addiction, abuse, or misuse before initiating treatment and re-assess all patients for the development of these conditions and behaviours. Assess for signs and symptoms of hypogonadism or hypoadrenalism; respiratory depression.
Overdosage
Symptoms: Somnolence, respiratory depression, hypotension, hypertension, tachycardia, hallucinations, seizures. In more severe cases, circulatory failure and deepening coma. Management: Supportive treatment. Employ adequate measures to maintain ventilation and general circulatory support. May consider gastric lavage and gastric aspiration. Administer IV naloxone for respiratory depression. May administer anticonvulsants as necessary.
Drug Interactions
Increased risk of serotonin syndrome with MAOIs. May enhance the CNS depressant effect with phenothiazines and TCAs. May antagonise the effect of strong opioid agonists (e.g. heroin, morphine). Potentially Fatal: Concomitant use with benzodiazepines or other CNS depressants (e.g. anxiolytics, non-benzodiazepine sedatives or hypnotics, muscle relaxants, tranquilisers, antipsychotics, general anaesthetics, other opioids) may lead to sedation, respiratory depression, and coma.
Food Interaction
Enhanced respiratory depression and sedative effect with alcohol.
Action
Description: Mechanism of Action: Pentazocine, a benzomorphan derivative, is an opioid analgesic that exhibits both opioid agonist and weak antagonist actions. It acts as an agonist at kappa opioid receptors and a partial agonist at μ receptors in the CNS, inhibiting ascending pain pathways and modifying the perception of and response to pain. Like opioids, pentazocine produces analgesia, sedation, and respiratory depression. Onset: 15-30 minutes (analgesia). Duration: Approx ≥3 hours (analgesia). Pharmacokinetics: Absorption: Well absorbed from the gastrointestinal tract. Time to peak plasma concentration: 1-3 hours. Distribution: Crosses the placenta. Plasma protein binding: Approx 50-75%. Metabolism: Metabolised in the liver mainly via oxidation into alcoholic and carboxylic acid metabolites and via glucuronide conjugation; undergoes extensive first-pass metabolism. Excretion: Via urine (small amounts as unchanged drug). Elimination half-life: Approx 2-3 hours.
Chemical Structure
Pentazocine Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 441278, Pentazocine. https://pubchem.ncbi.nlm.nih.gov/compound/Pentazocine. Accessed Feb. 25, 2025.
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