ULCOMET Film coated tablet Ref.[28254] Active ingredients: Cimetidine

Source: Υπουργείο Υγείας (CY)  Revision Year: 2019  Publisher: MEDOCHEMIE LTD, 1-10 Constantinoupoleos street, 3011 Limassol, Cyprus

5.1. Pharmacodynamic properties

Pharmacotherapeutic group: H2-receptor antagonist
ATC code: A02BA01

Mechanism of action

Cimetidine, one of the H2 blockers is a reversible, competitive antagonist of the actions of histamine on H2 receptors. It is highly selective in its action and is virtually without effect on H1 receptors or, indeed on receptors for other autacoids or drugs. The most prominent of the effects of histamine that are mediated by H2 receptors is stimulation of gastric acid secretion and they interfere remarkably little with physiological functions other than gastric secretion.

Cimetidine inhibits gastric acid secretion elicited by histamine or other H2 agonists in a dose-dependent, competitive manner; the degree of inhibition parallels the plasma concentration of the drug over a wide range. In addition, the H2 blockers inhibit gastric secretion elicited by muscarinic agonists or by gastrin, although this effect is not always complete.

This breadth of inhibitory effect is not due to non-specific actions at the receptors for these other secretagogues. Rather, this effect, which is noncompetitive and indirect, appears to indicate either that these two classes of secretagogues utilise histamine as the final common mediator or, more probably, that ongoing histaminergic stimulation of the parietal cell is important for amplification of the stimuli provided by ACh or gastrin when they act on their own discrete receptors. Receptors for all three secretagogues are present on the parietal cell. The ability of H2 blockers to suppress responses to all three physiological secretagogues makes them potent inhibitors of all phases of gastric acid secretion. Thus these drugs will inhibit basal (fasting) secretion and nocturnal secretion and also that stimulated by food, sham feeding, fundic distension, insulin, or caffeine. The H2 blockers reduce both the volume of gastric juice secreted and its hydrogen ion concentration. Output of pepsin, which is secreted by the chief cells of the gastric glands (mainly under cholinergic control), generally falls in parallel with the reduction in volume of the gastric juice. Secretion of intrinsic factor is also reduced, but it is normally secreted in great excess, and absorption of vitamin B12 is usually adequate even during long-term therapy with H2 blockers.

Concentrations of gastrin in plasma are not significantly altered under fasting conditions; however, the normal prandial elevation of gastrin concentration may be augmented, apparently as a consequence of a reduction in the negative feedback that is normally provided by acid.

5.2. Pharmacokinetic properties

Absorption

Cimetidine is rapidly and virtually completely absorbed. Absorption is little impaired by food or by antacids. Peak concentrations in plasma are attained in about 1 to 2 hours.

Distribution and biotransformation

Hepatic first-pass metabolism results in bioavailabilities of about 60% for cimetidine.

Elimination

The elimination half-life is about 2 to 3 hours.

Cimetidine is eliminated primarily by the kidneys and 60% or more may appear in the urine unchanged; much of the rest is oxidation products. Small amounts are recovered in the stool.

5.3. Preclinical safety data

Not available.

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