Pentazocine

How it works

It acts as a kappa-opioid receptor agonist with partial agonist or weak antagonist activity at the mu-opioid receptor.

Prescribing in practice

• As a mixed agonist–antagonist it can precipitate withdrawal in patients dependent on full mu-opioid agonists and may cause respiratory depression; avoid combining with other opioids.
• It can cause psychotomimetic effects such as hallucinations, dysphoria and confusion, and carries a risk of dependence and misuse.
• Use with caution in respiratory impairment, head injury, hepatic or renal impairment, and where it may raise cardiac workload.

Monitoring

Monitor pain control, sedation, respiratory and mental status, and watch for signs of dependence or withdrawal.

Counselling the patient

• This medicine can cause drowsiness; do not drive or operate machinery if affected.
• Avoid alcohol and tell your clinician about any other opioid medicines you take.
• Report hallucinations, severe drowsiness or difficulty breathing.

Evidence & guidelines

Pentazocine is a long-established opioid analgesic, though newer agents are often preferred owing to its psychotomimetic effects.