McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 4 0 Drugs affecting the female reproductive system

include ergometrine and oxytocin ( Syntocinon ) as well as combined ergometrine and oxytocin ( Syntometrine ). Therapeutic actions and indications The oxytocics directly affect neuroreceptor sites to stimulate contraction of the uterus. They are especially effective in the gravid uterus. Oxytocin, a synthetic form of the hypothalamic hormone, also stimulates the lacteal glands in the breast to contract, promoting milk ejection in breastfeeding women. Oxytocics are indicated for the prevention and treatment of uterine atony after birth. This is important to prevent postpartum haemorrhage. See Table 40.3 for usual indications for each of these drugs. Pharmacokinetics The oxytocics are rapidly absorbed after parenteral or oral administration, metabolised in the liver and excreted in urine and faeces. They cross the placenta and enter breast milk. The oxytocics are administered intramuscularly or intravenously. Contraindications and cautions Oxytocics are contraindicated in the presence of any known allergy to oxytocics to avoid hypersensitivity reactions and with cephalopelvic disproportion, unfav­ ourable fetal position, complete uterine atony or early pregnancy, which could be compromised by uterine stimulation . Caution should be used in women with coronary disease and hypertension due to the effect of causing arterial contraction, which could raise blood pressure or compromise coronary blood flow , or in women who have had previous caesarean births because of the effects on uterine contraction, which could compromise scars from previous procedures. Caution should be used in hepatic or renal impairment, which could alter the metabolism or excretion of the drug. Adverse effects The adverse effects most often associated with the oxytocics are related to excessive effects (e.g. uterine hypertonicity and spasm, uterine rupture, postpartum haemorrhage, decreased fetal heart rate). GI upset, nausea, headache and dizziness are also common. Ergo- metrine can produce ergotism, manifested by nausea, blood pressure changes, weak pulse, dyspnoea, chest pain, numbness and coldness in extremities, confu- sion, excitement, delirium, convulsions and even coma. Oxytocin has caused severe water intoxication with coma and even maternal death when used for a pro- longed period. This is thought to occur because of related effects of antidiuretic hormone (ADH), which is also stored in the posterior pituitary and may be released

Prototype summary: Oxytocin Indications: To initiate or improve uterine contractions for early vaginal delivery; to stimulate or reinforce labour in selected cases of uterine inertia; to manage inevitable or incomplete abortion; for second-trimester abortion; to control postpartum bleeding or haemorrhage; to treat breastfeeding deficiency. Actions: Synthetic form stimulates the uterus, especially the gravid uterus; causes myoepithelium of the lacteal glands to contract, resulting in milk ejection in breastfeeding women. Pharmacokinetics: Route Onset Peak Duration IV Immediate Unknown 60 mins IM 3–5 mins Unknown 2–3 hours T 1/2 : 1 to 6 minutes, with tissue metabolism and excretion in the urine. Adverse effects: Cardiac arrhythmias, hypertension, fetal bradycardia, nausea, vomiting, uterine rupture, pelvic haematoma, uterine hypertonicity, severe water intoxication, anaphylactic reaction. ■ ■ Assess for contraindications or cautions: history of allergy to oxytocics to avoid hypersensitivity reactions ; early status of pregnancy, which might lead to early onset of labour ; current status of breastfeeding; uterine atony, undesirable fetal position and cephalopelvic disproportion, which could be compromised by the stimulatory effects of the drug ; hypertension, which could be exacerbated due to the drug’s effect on arteries ; and history of caesarean birth, which could lead to uterine rupture or damage to previous surgical sites due to the drug’s stimulatory effect on uterine contraction. establish a baseline before beginning therapy and during therapy to evaluate drug effectiveness and to determine potential adverse effects. ■ ■ Assess the woman’s neurological status, including level of orientation, affect, reflexes and papillary response. ■ ■ Monitor vital signs, including pulse and blood pressure; auscultate lungs for evidence of adventitious sounds. ■ ■ Perform a complete physical assessment to Care considerations for women receiving oxytocics Assessment: History and examination