Pharmacology for Dentistry

262 Section 7/ Drugs Acting on GIT

MAGALDRATE

It is hydrated complex of hydroxy
magnesium aluminate. It initially reacts with
acid and releases Al(OH) 3 which then reacts
more slowly. It is a good antacid, with
prompt and sustained neutralizing action.

CALCIUM CARBONATE

It is a potent antacid with rapid acid
neutralizing capacity, but on long term use, it
can cause hypercalcemia, hypercalciuria and
formation of calcium stones in the kidney.

Every single compound among the
antacids have some serious side effects
especially when used for longer period or
used in elderly patients. To avoid these, the
antacids combinations are used such as:

i. Magnesium salts produce laxative

action while aluminium salts are

constipating in nature, so combination

of these two counteract their effect and

are used commonly.

ii. Fast acting antacid e.g. magnesium

hydroxide and slow acting antacid e.g.

aluminium hydroxide are used

together for sustained action.

iii. For reducing the systemic toxicity of

individual compounds.

ANTIULCER AGENTS

PATHOGENESIS OF PEPTIC ULCERS

Peptic ulcers are chronic, most often solitary
lesions that occur in any part of GIT exposed to
the aggressive action of acid-peptic juices.

Duodenal ulcer patients have an
increased capacity to secrete acid and
pepsin, increased responsiveness to stimuli
of acid secretion and more rapid gastric
emptying.

Gastric ulcer patients have a low to

normal levels of gastric acid, but never true

achlorhydria. Some primary defect in gastric

mucosal resistance is seen and also an

increased tendency to back diffusion of H+

ion. Other influences are thought to be

decreased production of bicarbonate buffer,

decreased blood flow which permits acid

ions to accumulate.

The various drugs used in peptic ulcer

are classified as in table 7.3.1.

H 2 RECEPTOR ANTAGONISTS

The H 2 antagonists in clinical use are analogs

of histamine that competitively inhibit the

interaction of histamine with H 2 receptors

and are highly selective. They inhibit gastric

acid secretion elicited by histamine and

other H 2 agonists in a dose dependent

manner. H 2 antagonists inhibit gastric acid

secretion by food and fundic distension and

also inhibit fasting and nocturnal acid

secretion and they reduce both the volume

and H+ ion concentration of gastric juice.

Pharmacokinetics

The H 2 antagonists are well absorbed

orally (60-80%) and its absorption is not

affected with the presence of food in the

stomach. They cross the placental barrier and

secreted mostly in mother’s milk. They are

excreted in urine mostly in unchanged form.

Adverse Reactions

They produces headache, dizziness, dry

mouth, rashes. CNS effects include

restlessness, delirium, hallucinations,

convulsion and coma. Intravenous bolus

injection cause bradycardia, arrhythmia and