Pentazocine injection is a synthetic narcotic analgesic derived from benzomorphan.
Its analgesic potency of 30 mg is said to be equal to 10 mg of morphine or 75 to 100 mg of pethidine.
The usual dose in adults is 20 to 60 mg i.m. (about 1 mg/kg). The oral dose ranges from 25 to 100 mg. Only 20% of the oral dose is absorbed.
Pentazocine injection effects
This drug may produce slight respiratory depression. This respiratory depression is not reversed by specific narcotic antagonists, but by nikethamide, methylphenidate and naloxone. Pentazocine produces analgesia and sedation.
Pentazocine injection also causes an increase in the blood pressure. Asthmatic patients who are sensitive to aspirin may be also sensitive to it.
It has no addictive activity. Typical physical dependence is also rare. It produces little or no euphoria but dysphoria may occur. It does not affect pupillary size and intraocular tension.
It is a mild narcotic antagonist (about one-fiftieth the activity of nalorphine) as well as agonist. It is therefore classified as partial agonist or opioid agonist/antagonist. It causes little nausea, vomiting or constipation. It crosses the placenta less.
High doses can cause unpleasant hallucinations. It is less cumulative and is mostly metabolized in the body. It can antagonize respiratory depression caused by fentanyl yet allow continuing analgesia.