C H A P T E R 5 7
Drugs affecting gastrointestinal secretions
903
diarrhoea or constipation; central nervous system (CNS)
effects of dizziness, headache, somnolence, confusion or
even hallucinations (thought to be related to possible H
2
receptor effects in the CNS); cardiac arrhythmias and
hypotension (related to H
2
cardiac receptor blocking;
more commonly seen with intravenous or intramuscular
administration or with prolonged use); and gynaeco-
mastia (more common with long-term use of cimetidine)
and impotence.
Clinically important drug–drug interactions
Cimetidine, famotidine and ranitidine can slow
the metabolism of the following drugs, leading to
increased serum levels and possible toxic reactions:
warfarin anticoagulants, phenytoin, beta-adrenergic
blockers, alcohol, quinidine, lignocaine, theophylline,
chloroquine, benzodiazepines, nifedipine, tricyclic anti-
depressants, procainamide and carbamazepine. There is
a risk of increased salicylate levels if nizatidine is taken
with aspirin.
Monitor for drug–drug interactions as listed.
Evaluate the effectiveness of the teaching program.
Evaluate the effectiveness of comfort and safety
measures.
TEACHING FOR W.T.
• The drug that has been prescribed for you, ranitidine, is
called a histamine-2 antagonist. A histamine-2 antagonist
decreases the amount of acid that is produced in the
stomach. It is used to treat conditions that are aggravated
by excess acid.
• Some of the following adverse effects may occur with
this drug:
•
Diarrhoea
: Have ready access to bathroom facilities.
This usually becomes less severe over time.
•
Dizziness, headache
: These usually lessen as your body
adjusts to the drug. Change positions slowly. If you feel
drowsy, avoid driving or dangerous activities.
• Report any of the following to your healthcare provider
:
sore throat, unusual bleeding or bruising, confusion, muscle
or joint pain, tarry stools.
• Avoid taking any OTC medication without first checking
with your healthcare provider. Several of these medications
can interfere with the effectiveness of this drug.
• If an antacid has been ordered for you, take it exactly as
prescribed, spaced apart from your ranitidine.
• Tell any doctor, nurse or other healthcare provider
involved in your care that you are taking this drug.
• If you are taking any other medications, do not vary the
drug schedules. Consult with your primary healthcare
provider if anything should happen to change any of
these drugs or your scheduled doses.
• It is important to have regular medical follow-up while
you are taking this drug to evaluate your response to the
drug and any possible underlying problems.
• Keep this drug, and all other medications, out of the reach
of children.
Prototype summary: Cimetidine
Indications:
Short-term treatment of active duodenal
or benign gastric ulcers; treatment of pathological
hypersecretory conditions; prophylaxis of stress-
induced ulcers; treatment of erosive gastro-
oesophageal reflux; relief of symptoms of heartburn
and acid indigestion.
Actions:
Inhibits the actions of histamine at H
2
receptor sites of the stomach, inhibiting gastric acid
secretion and reducing total pepsin output.
Pharmacokinetics:
Route Onset
Peak
Duration
Oral
Varies
1–1.5 hours 4–5 hours
IM, IV Rapid
1–1.5 hours 4–5 hours
T
1/2
:
2 hours; metabolised in the liver and excreted
in urine.
Adverse effects:
Dizziness, confusion, headache,
somnolence, cardiac arrhythmias, cardiac arrest,
diarrhoea, impotence, gynaecomastia, rash.
Care considerations for
people receiving histamine-2 antagonists
Assessment: History and examination
■
■
Assess for
possible contraindications or cautions
:
history of allergy to any H
2
antagonists
to prevent
potential allergic reactions
; impaired renal or
hepatic function,
which could affect metabolism
and excretion of the drug
; a detailed description
of the GI problem, including length of time of
the disorder and medical evaluation,
to evaluate
the appropriate use of the drug and possibility
of underlying medical problems
; and current
status of pregnancy or breastfeeding
because of
the potential for adverse effects on the fetus or
newborn.
■
■
Perform a physical examination
to establish
baseline data before beginning therapy, determine
effectiveness of the therapy and evaluate for any
adverse effects associated with drug therapy.
