Labour and Birth Case Drugs

Question 1

Gas and air (entonox)

Answer 1

Mechanism:
○Nitrous oxide and oxygen.
○Exact NO mechanism unknown, induces opioid peptide release in the brain stem.
○Leads to the activation of descending noradrenergic neurones, and modulation of the nociceptive process in the spinal cord.
○Active on many receptors such as dopamine and adrenoreceptors.

Effects:
○Reduction in pain sensitivity.
○Improves Oxygenation.

Side Effects:
○Dizziness
○Nausea
○‘Tingling’ Feeling

Question 2

Pethidine

Answer 2

Mechanism:
○Opiate receptors coupled with G-protein receptors.
○Opiate binding stimulates exchange of GDP to GTP on G-protein complex.
○Stimulates inhibition of adenylate cyclase, decreasing intracellular cAMP.
○Inhibits release of nociceptive neurotransmitters such as substance P, GABA, dopamine, acetylcholine and noradrenaline.
○Opioids also inhibit the release of vasopressin, somatostatin, insulin and glucagon.
○Opioids close N-type voltage-operated calcium channels and open calcium-dependent inward potassium channels.
○This results in hyperpolarization and reduced neuronal excitability.

Effects:
○Analgesic
○Sedative

Side Effects:
○Can lead to morphine-like dependence.
○Nausea
○Dizziness

Question 3

Epidural

Answer 3

• Epidural analgesia is an injection of local anaesthetic alone.
• Bupivacaine is a local anaesthetic that stabilises the neuronal membrane and prevents the initiation and transmission of nerve impulses.
• For most women, an epidural gives complete pain relief. It can be helpful for women who are having a long or particularly painful labour.
• However epidurals can only be given by an anaesthetist.
• May prolong labour.

Question 4

Prostaglandins

Answer 4

●Mechanism:
○Bind smooth muscle cells in uterine lining
○Results in degradation of collagen in the connective tissue of the stroma.
○Also reduce cervical tone due to increased amplitude and frequency of contractions
○Uterotonic qualities can help reduce PP bleeding.
○Ultimately ‘ripen’ the uterus to prepare for childbirth.
○Delivered via gel or pessary.
○Lots of contraindications with magnesium compounds e.g. Mg Citrate – over the counter laxative.

●Effects:
○‘Ripening’ of cervix.
○Increased amplitude and frequency of contractions.

●Side Effects:
○D&V
○Dehydration
○Vaginal Bleeding/Spotting
○Menstrual Cramps

Question 5

Oxytocin

Answer 5

Mechanism:
○Conc’n of oxytocin receptors on myometrium increases in pregnancy and peaks in early labour.
○Activation of receptors triggers cascade that leads to increased intracellular Ca2+ in uterine myofibrils, strengthens and increases frequency of contractions.
○Regulated by positive feedback.
○Head of foetus pushing on the cervix signals release of oxytocin from the posterior pituitary of the mother.
○Travels to uterus and stimulates uterine contractions.
○Elicited uterine contractions will then stimulate the release of increasing amounts of oxytocin. Positive feedback loop continues until parturition (birth).
○This is simulated in practice by slowly increasing the dosage of oxytocin over several hours.

●Effects:
○Increased rate and intensity of uterine contractions.

●Side Effects:
○Cardiac Arrythmia
○Convulsion
○Abdominal Pain
○Light-headedness & Syncope