Pethidine, also known as meperidine, is a synthetic opioid analgesic that has been a staple in obstetric practice across Nigeria for decades. It acts primarily as a mu-opioid receptor agonist within the central nervous system, altering both the perception of pain and the emotional response to it. Unlike morphine, pethidine possesses a chemical structure similar to atropine, which gives it mild anticholinergic properties. Because of this, it does not cause the same degree of smooth muscle spasm as some other opioids, though it remains a potent systemic pain reliever during the first stage of labor.
Administering pethidine requires precise timing to be effective without harming the newborn. It is typically reserved for the first stage of labor when contractions are regular, painful, and the cervix is progressing well, usually before four to five centimeters of dilation in a nulliparous woman.
If given too early, it can slow down uterine contractions and prolong labor. Conversely, if given too close to delivery—typically within two hours of birth—the drug crosses the placenta and peaks in the fetal circulation just as the baby is born, leading to severe neonatal respiratory depression.
Pethidine can be given through various routes depending on the urgency and clinical setting.
Midwives must always check the baseline respiratory rate and blood pressure before administration.
While pethidine provides much-needed relief, it carries significant side effects for both mother and baby.
Maternal side effects include nausea, vomiting, drowsiness, dizziness, and delayed gastric emptying, which increases the risk of aspiration if general anesthesia becomes necessary.
Neonatal side effects stem from placental transfer. Babies exposed to pethidine often experience neonatal respiratory depression, poor feeding reflexes, and a reduced Apgar score at birth. Its active metabolite, norpethidine, has a long half-life in newborns and can cause sedation that lingers for several days.
Safe administration of pethidine demands vigilant midwifery oversight. Midwives must monitor maternal vital signs—specifically respiratory rate, pulse, and blood pressure—every thirty minutes after administration until the peak effect passes.
Crucially, naloxone must always be immediately available in the labor ward. Naloxone is a specific opioid antagonist used to reverse severe respiratory depression in either the mother or the newborn. For a compromised newborn, naloxone can be administered via intramuscular injection or through an endotracheal tube if resuscitation is required, alongside standard bag-valve-mask ventilation.