Pharmacology for Dentistry

Emetics & Antiemetic Agents 259

METOCLOPRAMIDE

It is a centrally acting dopamine antagonist
and acts on CTZ by blocking D 2 receptors
thereby preventing emesis. It also acts
peripherally in GIT to enhance ACh release
from muscarinic receptors, leading to
increased gastric peristalsis and relaxing the
pylorus and first part of duodenum. Thus it
increases gastric emptying. It also increases
tone of lower esophageal sphincter and
prevents gastroesophageal reflux.

It is absorbed orally, partly conjugated
in liver and excreted in urine.

It is used as antiemetic, for gastroesoph-
ageal reflux disease, dyspepsia and as gas-
trokinetic.

Adverse effects include drowsiness,
diarrhoea, facial spasm, trismus, oculogyric
crisis seen commonly in children and young
adults.

On prolonged use leads to tardive
dyskinesia in elderly, gynaecomastia,
galactorrhoea and parkinsonism.

5-HT^3 ANTAGONISTS

ONDANSETRON

It causes antiemetic effect by blocking
5-HT 3 receptor in brain and periphery.

Absorbed orally and bioavailability is
60-70% due to first pass metabolism.
Metabolised by hydroxylation and
metabolites are excreted in urine and faeces.

It is used in nausea and vomiting
induced by cytotoxic chemotherapy and
radiotherapy and for the prevention of
postoperative vomiting.

Side effects include headache,

constipation, dizziness and allergic reactions.

GRANISETRON

It is newer compound. Mechanism of

action is similar to ondansetron but can

cause elevation of liver enzyme level e.g.

SGOT, SGPT etc. It is mainly used in the

management of nausea and vomiting

induced by cytotoxic chemotherapy and

radiotherapy.

Dolasetron is a new compound of the

similar category acting by blocking 5-HT 3

receptor.

PROKINETIC AGENTS

CISAPRIDE

It is a selective 5-HT 4 agonist. It restores

and increases motility throughout

gastrointestinal tract. It appears to increase

the release of acetylcholine from myenteric

plexus of the gut.

It is absorbed orally (bioavailability 33%)

and is metabolised in liver.

Adverse effects include abdominal

cramps, diarrhoea, headache, convulsions

and extrapyramidal effects. When used with

imidazole antifungals/macrolide

antibiotics, it may lead to Q-T prolongation

and ventricular arrhythmias.

It is indicated in non-ulcer dyspepsia

and gastroesophageal reflux disease and not

mainly used as antiemetic.

MOSAPRIDE

Mosapride is a selective 5-HT 4 receptor

agonist which is free from the extrapyrami-

dal and proarrhythmic effects. It stimulates