256 Section 7/ Drugs Acting on GITABSORBENTS AND BULK FORMING DRUGSThey are colloidal bulk forming agents which
swell by absorbing water. They modify the
consistency and frequency of stools. They are
used for functional bowel disease associated
with diarrhoea. They are safe substances but
their effect occurs slowly.
ANTIMOTILITY AND ANTISECRETORY DRUGSAntimotility drugs are opioid drugs. They
increase small bowel smooth muscle tone and
segmentation activity. They also reduce
propulsive movements and decrease intestinal
secretions while increasing absorption. They
mediate these actions through μ receptors.
LOPERAMIDE
It has a direct action on intestinal muscu-
lature and having a weak anticholinergic
property. It is used to treat acute and chronic
diarrhoea. Adverse effects include
addominal cramps and skin rash.
DIPHENOXYLATE
Chemically it is an opioid, related to
pethidine. It is used in acute and chronic
diarrhoea but since it crosses the blood brain
barrier it can cause CNS effect similar to
opioids. Atropine is added with diphenoxylate
(LOMOFEN) to discourage abuse.
Loperamide and codeine are preferred to
diphenoxylate in chronic diarrhoea, because
they have less tendency to produce drug
dependence. Long-term use of these drugs may
aggravate irritable bowel syndrome. These
drugs are used cautiously in attacks of colitis
because there is increased risk of toxic
megacolon. Also all these drugs should be used
with caution in elderly because faecal impaction
may occur leading to abdominal obstruction.
These are usually not prescribed for bacterial
diarrhoea in children because by delaying the
passage of liquid faeces there is proliferation of
pathogens which is undesirable.SULFASALAZINE
It is an antisecretory drug. It is 5-ami-
nosalicylic acid with linked sulfapyridine
through azo bond. The drug is poorly ab-
sorbed from the intestine and the azo link-
age is broken down by the bacterial flora in
the distal ileum and colon to release 5-ami-
nosalicylic acid (5-ASA) and sulfapyridine.
5-ASA inhibits locally prostaglandin synthe-
sis, decreases mucosal secretion. It is used
in rheumatoid arthritis and ulcerative coli-
tis. Side effects include fever, rashes, blood
dyscrasias, nausea, vomiting and headache.MESALAZINE
5-ASA is prepared as delayed release
preparation by coating with acrylic polymer,
which releases 5-ASA in distal ileum and colon.
It is used in ulcerative colitis to prevent relapses.
Olsalazine and balsalazine are the
newer compounds of 5-aminosalicylic acid
linked with azo bonds.ANTIMICROBIAL THERAPY
Antimicrobials have a limited role in
treatment of diarrhoea because only a small
percentage of diarrhoeas are caused by
bacterial infection. Majority of cases are due
to non infective causes, Rota virus and food
poisoning in which antimicrobial therapy
has no role.
Specific antimicrobial drugs are discussed
in chapter ‘Chemotherapeutic agents.’