A Textbook of Clinical Pharmacology and Therapeutics

After prolonged use of stimulant laxatives, the colon
becomes dilated and atonic with diminished activity. The cause
is not clear, but this effect is perhaps due to damage to the
intrinsic nerve plexus of the colon. The disorder of bowel motil-
ity may improve after withdrawing the laxative and using a
high-residue diet.
Some people, mainly women, take purgatives secretly. This
probably bears some relationship to disorders such as anorexia
nervosa that are concerned with weight loss, and is also associ-
ated with self-induced vomiting and with diuretic abuse. The
clinical and biochemical features can closely mimic Bartter’s
syndrome and this possibility should always be investigated in
patients in whom the diagnosis of this rare disorder is enter-
tained, especially adults in whom true Bartter’s syndrome
almost never arises de novo. Features include:

• sodium depletion – hypotension, cramps, secondary
  hyperaldosteronism;


• potassium depletion – weakness, polyuria and nocturia
  and renal damage.

In addition, there may be features suggestive of enteropathy
and osteomalacia.
Diagnosis and treatment are difficult; melanosis coli may
provide a diagnostic clue. Urinary electrolyte determinations
may help, but can be confounded if the patient is also surrep-
titiously taking diuretics.

preparations (such as Dioralyte®or Electrolade®), which contain

electrolytes and glucose. Antibiotic treatment is indicated

for patients with systemic illness and evidence of bacterial

infection.

Adjunctive symptomatic treatment is sometimes indicated.

Two main types of drug may be employed, that either

decrease intestinal transit time or increase the bulk and viscos-

ity of the gut contents.

DRUGS THAT DECREASE INTESTINAL TRANSIT TIME

OPIOIDS

For more information on opioid use, see Chapter 25.

Codeine is widely used for this purpose in doses of

15–60 mg. Morphineis also given, usually as a kaolinand

morphinemixture. Diphenoxylateis related to pethidineand

also has structural similarities to anticholinergic drugs. It may

cause drug dependence and euphoria and is usually pre-

scribed as ‘Lomotil’ (diphenoxylate plus atropine). Overdose

with this drug in children causes features of both opioid and

atropine intoxication and may be fatal.

LOPERAMIDE

Loperamide is an effective, well-tolerated antidiarrhoeal

agent. It antagonizes peristalsis, possibly by antagonizing

acetylcholine release in the intramural nerve plexus of the gut,

although non-cholinergic effects may also be involved. It is

poorly absorbed and probably acts directly on the bowel. The

dose is 4 mg initially, followed by 2 mg after each loose stool

up to a total dose of 16 mg/day. Adverse effects are unusual,

but include dry mouth, dizziness, skin rashes and gastric dis-

turbances. Excessive use (especially in children) is to be

strongly discouraged.

DRUGS THAT INCREASE BULK AND VISCOSITY

OF GUT CONTENTS

Adsorbents, such as kaolin, are not recommended for diar-

rhoea. Bulk-forming drugs, such as ispaghula,methylcellu-

loseandsterculiaare useful in controlling faecal consistency

in ileostomy and colostomy, and in controlling diarrhoea asso-

ciated with diverticular disease.

TRAVELLERS’ DIARRHOEA

This is a syndrome of acute watery diarrhoea lasting for one to

three days and associated with vomiting, abdominal cramps

and other non-specific symptoms, resulting from infection

by one of a number of enteropathogens, the most common

being enterotoxigenic Escherichia coli. It probably reflects colo-

nization of the bowel by ‘unfamiliar’ organisms. Because of the

variable nature of the pathogen, there is no specific treatment.

258 ALIMENTARY SYSTEM ANDLIVER

Case history

A 70-year-old woman who was previously very active but

whose mobility has recently been limited by osteoarthritis

of the knees and hips sees her general practitioner because

of a recent change in bowel habit from once daily to once

every three days. Her current medication includes regular

co-codamol for her osteoarthritis, oxybutynin for urinary

frequency, aluminium hydroxide prn for dyspepsia, and

bendroflumethiazide and verapamil for hypertension.

Following bowel evacuation with a phosphate enema,

proctoscopy and colonoscopy are reported as normal.

Question

Which of this patient’s medications may have contributed

to her constipation?

Answer

• Co-codamol, which contains an opioid–codeine
  phosphate.


• Aluminium hydroxide.


• Bendroflumethiazide.


• Verapamil.


• Oxybutynin (an anticholinergic).

DIARRHOEA

The most important aspect of the treatment of acute diarrhoea
is the maintenance of fluid and electrolyte balance, particularly
in children and in the elderly. In non-pathogenic diarrhoea or
viral gastroenteritis, antibiotics and antidiarrhoeal drugs are
best avoided. Initial therapy should be with oral rehydration