Pentazocine

There is no epidemiological evidence for the safety of pentazocine in human pregnancy, but it has been widely used for many years without apparent ill consequences. Doses which produce maternal toxicity in rats have caused harmful effects in the foetus. Pentazocine can rapidly cross the placental barrier and enter the foetal circulation and has the potential to cause opioid effects including central depression and abstinence syndrome in the foetus and newborn infant. It does not appear to have significant adverse effects on uterine function at parturition. Nonetheless, careful consideration should be given to the use of pentazocine during pregnancy, particularly during the first trimester, or at term. Special attention should be paid to clinical monitoring of the newborn, particularly premature infants, if pentazocine has been used during labour.

Pentazocine is excreted in very small amounts in breast milk. Caution should therefore be observed in administering pentazocine to breast-feeding mothers, particularly of infants at risk.

It is recommended that infants of nursing mothers who are receiving high doses of pentazocine, be appropriately monitored.

As pentazocine may produce sedation, dizziness and occasionally euphoria, so ambulant patients should be warned against the performance of potentially hazardous tasks such as driving a car or not operating machinery. Alcohol may potentiate the sedative effect.

This medicine can impair cognitive function and can affect a patient’s ability to drive safely. This class of medicine is in the list of drugs included in regulations under 5a of the Road Traffic Act 1988. When prescribing this medicine, patients should be told:

• The medicine is likely to affect your ability to drive
• Do not drive until you know how the medicine affects you
• It is an offence to drive while under the influence of this medicine
• However, you would not be committing an offence (called ‘statutory defence’) if:
• The medicine has been prescribed to treat a medical or dental problem and
• You have taken it according to the instructions given by the prescriber and in the information provided with the medicine and
• It was not affecting your ability to drive safely