C H A P T E R 4 0
Drugs affecting the female reproductive system
621
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.
Care considerations for
women receiving oxytocics
Assessment: History and examination
■
■
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.
■
■
Perform a complete physical assessment
to
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.
