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Drugs acting on the gastrointestinal system
response. Drowsiness, dizziness, weakness, tremor
and headache are common adverse effects. Other, not
uncommon adverse effects include hypotension, hyper-
tension and cardiac arrhythmias. Autonomic effects
such as dry mouth, nasal congestion, anorexia, pallor,
sweating and urinary retention often occur with phe-
nothiazines. People should be cautioned that their urine
may be tinged pink to red-brown. This is a drug effect
but can cause concern if the person is not expecting it.
Endocrine effects such as menstrual disorders, galac-
torrhoea and gynaecomastia have been reported with
phenothiazine use.
Photosensitivity
(increased sen-
sitivity to the sun and ultraviolet light) is a common
adverse reaction with these antiemetics. People should
be advised to use sunscreens and protective garments if
exposure cannot be avoided.
Clinically important drug–drug interactions
Additive CNS depression can be seen with any of the
antiemetics if they are combined with other CNS
depressants, including alcohol. People should be advised
to avoid this combination and any OTC preparation
unless they check with their healthcare provider. Other
drug–drug interactions are specific to each drug (refer to
a nursing or midwifery drug guide).
O
ther dopamine
D
2
receptor antagonists
Two other non-phenothiazine dopamine D
2
receptor
antagonists currently available for use as antiemet-
ics are metoclopramide (
Maxolon
) and domperidone
(
Motilium
). These act to reduce the responsiveness of
the nerve cells in the CTZ to circulating chemicals that
induce vomiting. Chapter 58 discusses metoclopramide,
which is also commonly used to treat gastroparesis, in
greater detail.
•
Dehydration
: Avoid excessive heat exposure, and try to
drink fluids as much as possible, because you will have
an increased risk of heat stroke.
• Report any of the following conditions to your
healthcare provider:
fever, rash, yellowing of the eyes or
skin, dark urine, pale stools, easy bruising, rash and vision
changes.
• Avoid over-the-counter (OTC) medications. If you feel
that you need one, check with your healthcare provider
first.
• Tell any doctor, nurse or other healthcare provider that
you are taking this drug.
• Keep this drug and all medications out of the reach of
children.
Prototype summary: Prochlorperazine
Indications:
Control of severe nausea and vomiting.
Actions:
Mechanism of action not understood;
depresses various areas of the CNS, including the
CTZ in the medulla.
Pharmacokinetics:
Route Onset
Peak
Duration
Oral
30–40 mins Unknown 3–4 hours
Rectal 60–90 mins Unknown 3–4 hours
IM 10–20 mins 10–30 mins 3–4 hours
IV Immediate 10–30 mins 3–4 hours
T
1/2
:
Unknown; metabolised in the liver and excreted
in urine.
Adverse effects:
Drowsiness, dystonia, photophobia,
blurred vision, urine discoloured pink to red-
brown.
Prototype summary: Metoclopramide
Indications:
Prevention of nausea and vomiting
associated with emetogenic cancer chemotherapy;
prevention of postoperative nausea and vomiting.
Actions:
Slows GI activity; sedating.
Pharmacokinetics:
Route Onset
Peak
Duration
Oral
30–60 mins 60–90 mins 1–2 hours
IM 10–15 mins 60–90 mins 1–2 hours
IV 1–3 mins
60–90 mins 1–2 hours
T
1/2
:
5–6 hours; metabolised in the liver and
excreted in urine.
Adverse effects:
Drowsiness, fatigue, restlessness,
extrapyramidal symptoms, diarrhoea.
5-HT
3
receptor blockers
The 5-HT
3
receptor blockers block those receptors asso-
ciated with nausea and vomiting in the CTZ and locally.
These drugs include dolasetron (
Anzemet
), granisetron
(
Kytril
), ondansetron (
Zofran
), palonosetron (
Aloxi
)
and tropisetron (
Navoban
).
Therapeutic actions and indications
The 5-HT
3
receptor blockers have proven especially
helpful in treating the nausea and vomiting associated
with antineoplastic chemotherapy, radiation therapy,
and postoperative nausea and vomiting. They are specific
for the treatment of nausea and vomiting associated
