Pirenzepine anticholinergic

Pirenzepine is an anticholinergic drug with selective effects on muscarinic Mi receptors. It therefore inhibits gastric acid secretion in the stomach. When it was introduced it was claimed that in the doses necessary to affect gastric acid secretion it would be almost entirely free of other muscarinic (atropine-like) effects. However, although muscarinic adverse effects, such as dry mouth and difficulty in accommodation, are less common with pirenzepine than with atropine, they can still occur in about half the patients who take the drug (1). Cardiac conduction effects resulting in sinus tachycardia, atrial fibrillation, and nodal tachycardia can also occur. 

Telenzepine is a muscarinic Mi receptor antagonist, like pirenzepine. On a weight-for-weight basis it is 25-50 times more potent than pirenzepine, but dose for dose it is, if anything, more likely to have undesired anticholinergic effects (1). 

Anticholinergic drugs are only really suitable in the case of agents that show some gastric-selectivity, e.g. pirenzepine and telenzepine (see MUSCARINIC CHOLINOCEPTOR antagonists). They work by reducing the secretion of peptic acid by the stomach mucosa. 

Anticholinergics such as atropine are now believed to act on both M, and M2 cholinergic receptors, accounting for both its antisecretory (Mi) and other anticholinergic properties such as ocular, bladder, and salivary side effects (M2). As mentioned earlier, the benzodiazepine compound pirenzepine is highly MI specific. At doses that inhibit HC1 secretion these side effects are not a significant problem. Although not necessarily more effective than cimetidine (see later), it is effective in otherwise treatment-resistant peptic... 

Pirenzepine hydrochloride is found to retard gastric secretion appreciably with minimal systemic anticholinergic eifects. Hence it has been successfully employed for the management and treatment of hyperacidity and peptic ulcer. 

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