Pethidine is a widely used drug for pain relief in labour. Pethidine is a similar drug to morphine and heroin. These three drugs are from a family of drugs known as opioids. Opioids basically are morphine-like drugs. Morphine is a natural drug that can be extracted from the opium poppy, whereas pethidine is synthetically made. Pethidine was first used in Germany in 1940 to reduce pain in labour and its use has continued to the present day. Initially, when pethidine was created, it was thought to be non-addictive but we now know that this is not true.

Pethidine works by mimicking the effects of endorphins – the body’s own morphine-like substances. One of the functions of endorphins is to act as the body’s natural pain killer. Pethidine (like endorphins) attaches to special sites on the outside of nerve cells. These sites are known as opioids receptors. Once pethidine attaches to these receptors, a chain of events occurs that results in the depression of normal activity for a little while. Pethidine’s effects are far more dramatic than endorphins.

The effects pethidine has on a woman’s body can readily be observed after it has been administered. A woman may become dizzy, and drowsy, her eyes may change in appearance and she may experience an altered level of perception of events around her. Pethidine acts on the central nervous system by inhibiting the pain signals that are sent to the brain. The subsequent result can reduce the pain experienced by the woman in labour. Pethidine can also increase the amount of pain a woman can tolerate.

How is pethidine given to a woman when she is in labour?

The most common way that pethidine is given to a woman in labour is by an injection into the muscle (usually into the thigh or buttock). Occasional pethidine is given into a vein via a drip. Pethidine usually has to be ordered by a doctor but is then given by a midwife. The dosage a woman receives in labour varies, usually ranging from 50mg to 100mg. The total volume injected into the muscle is one to two millilitres.

How long does pethidine work for?

If pethidine is given via an injection into the muscle, it usually takes around ten to twenty minutes to begin working. Pethidine’s effects, when given by this method, last two to three hours. If pethidine is given directly into a vein via a drip, the effects are a lot more rapid. Pethidine begins working within two to three minutes. When pethidine is given via a vein it enters the bloodstream directly and only takes a couple of minutes to circulate around the entire body, therefore pethidine reaches the brain and the nerve sites rapidly. The problem with giving pethidine directly into a vein is even though the effects are rapid, they only last for a short time. The effects of pethidine injected into a muscle last a lot longer.

Will pethidine provide me with adequate pain relief while I am in labour?

This is not an easy question to answer as women report varying responses to pethidine. Some women say that it provides adequate relief while other women say they achieved no pain relief whatsoever (48% of women in one survey said this). Women report pethidine provides greater relief in early labour rather than in later labour (when the contractions are a lot stronger). The bigger the dose of pethidine, the more effective the pain relief. But the bigger the dose, the more side effects a woman and her baby may experience.

One piece of research said that pethidine does not provide adequate pain relief during labour, but ends up heavily sedating the woman. Overall pethidine may reduce pain experienced during labour in some women. If a woman is tired, pethidine can provide sedation (and sometimes much-needed sleep). Pethidine can act as a muscle relaxant which can in some cases result in faster dilation (opening) of the cervix.

What are the disadvantages of using pethidine for pain relief in labour?

Pethidine may not provide adequate pain relief for some women. Nausea and vomiting are common, you may mix the medication with pethidine to help reduce these effects. Some women report feeling drowsy and confused. The effects pethidine has on perception may make contractions difficult to deal with. Other potential side effects for the woman in labour include difficulty passing urine, dry mouth, hallucinations, respiratory depression, low blood pressure and allergic reaction.

There are no advantages to the baby if the mother has pethidine. Pethidine is known to cross the placenta and is present in breast milk. The major problem for the baby is that pethidine can cause breathing difficulties after birth due to its depressive effect on the baby’s respiratory centre. These effects are worse if the baby is born one to three hours after an injection of pethidine has been given. This is the reason that pethidine is ideally avoided when the birth is perceived to be close.

An antidote can be given to the baby to reverse the effects of pethidine, however, the effects of the antidote only last a short time and when they wear off the baby may re-experience breathing problems. Babies are more likely to have jaundice if their mothers have pethidine. Pethidine affects the baby’s sucking reflex and can cause breastfeeding difficulties for the first few days. Babies may require special care or neonatal intensive care from the effects of pethidine, resulting in the separation of mother and baby.

Reference List

• Guy Hospital. (1994). 1994 Nursing drug reference 2nd ed. Mosby: London.
• Robertson, A. (1999). Preparing for birth: Mothers. ACE Graphics: Sydney.
• home.intekom.com/pharm/quatrom/q-pethid.html
• www.manbit.com/obstetpain/peth2.htm – (Website no longer active)
• www.manbit.com/obstetpain/peth3.htm – (Website no longer active)
• www.manbit.com/obstetpain/peth4.htm – (Website no longer active)
• www.manbit.com/obstetpain/peth5.htm – (Website no longer active)
• www.manbit.com/obstetpain/peth6.htm – (Website no longer active)
• www.qub.ac.uk/nur/research/rogan.html – (Website no longer active)

(25th June 2000)