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Pirenzepine (ATC A02BX03) is an M1-selective muscarinic receptor antagonist used mainly for peptic ulcer disease and related upper gastrointestinal disorders, whose anticholinergic profile and documented excretion into breast milk make it toxicologically unsuitable during lactation.file+4

Classification and indications

Pirenzepine belongs to the ATC class A02BX03 (other drugs for peptic ulcer and gastro‑oesophageal reflux disease) and is marketed, for example, under the trade name Gastrozepin. It is indicated for gastric and duodenal ulcer and upper dyspepsia, historically as monotherapy or as part of combination regimens for ulcer healing, and in some regions has been used off‑label to manage antipsychotic‑induced hypersalivation.drugbank+5

Mechanism of action and pharmacodynamics

Pirenzepine is a selective muscarinic M1 receptor antagonist that preferentially acts on the gastric mucosa to inhibit basal and stimulated secretion of gastric acid and pepsin. By reducing acetylcholine‑mediated parasympathetic activity in the upper gastrointestinal tract, it decreases gastric motility and can delay gastric emptying, while its limited penetration of the blood–brain barrier spares central cholinergic function at usual doses.wikipedia+3

General pharmacokinetics

Orally, pirenzepine shows relatively low bioavailability (around 20–30%), which decreases further if the drug is taken with or after meals rather than on an empty stomach. Plasma protein binding is low (about 12%), its elimination half‑life is approximately 12 hours, and excretion is predominantly fecal, with only a minor fraction eliminated unchanged in urine. These characteristics support twice‑daily dosing in standard ulcer regimens and allow therapy to extend over weeks to months when clinically required.drugs.ncats+2

Dosage and duration of standard therapy

In adults, typical dosage regimens for ulcer therapy use 100 mg/day (one tablet in the morning and one at night, half an hour before meals), with the possibility to increase to 150 mg/day in divided doses for severe symptoms. Freedom from ulcer discomfort usually occurs within days, but therapy is recommended to continue for 4–6 weeks to ensure mucosal healing, and may be prolonged up to three months in selected cases.publishing.service

Adverse effects and contraindications

Adverse effects are principally anticholinergic and include dry mouth, blurred vision, constipation, urinary retention, tachycardia, headache, and, at higher exposures or in predisposed patients, mental confusion or cognitive changes. Because of these effects, pirenzepine should be avoided or used with great caution in patients with prostatic enlargement, organic pyloric stenosis or paralytic ileus, narrow‑angle glaucoma or shallow anterior chamber, severe cardiac arrhythmias, and terminal chronic kidney disease.pubmed.ncbi.nlm.nih+3

Toxicology and overdose

Pirenzepine’s toxicological profile is dominated by dose‑dependent anticholinergic effects that can progress from mucosal dryness and visual disturbance to more serious gastrointestinal and cardiac manifestations. In overdose, reported symptoms include intense dry mouth, marked visual disturbance, diarrhoea or constipation, headache, and mental confusion; there is no specific antidote, and management relies on early gastric decontamination when appropriate and symptomatic–supportive care (including close cardiovascular and neurological monitoring).sciencedirect+3

Lactation pharmacokinetics

Pirenzepine has a moderate molecular weight (around 351 Da), low protein binding, and a half‑life of about 12 hours, a combination that favours some transfer into breast milk and maintenance of measurable infant exposure over time. Regulatory product information explicitly states that pirenzepine appears in the milk of lactating mothers in minimal amounts, but quantitative infant plasma or milk:plasma ratio data are not available, and standard lactation references do not list it as a preferred or well‑studied agent.pubchem.ncbi.nlm.nih+4

Potential effects in breastfed infants

Even if milk levels are described as minimal, anticholinergic agents can have disproportionate effects in neonates and young infants due to immature autonomic control and cardiac electrophysiology. Excessive anticholinergic exposure in this age group theoretically carries a risk of severe arrhythmias, including torsade‑like ventricular tachycardia and sudden cardiac death, especially in vulnerable infants (e.g. premature, cardiac disease, electrolyte disturbances).medsafe+2

Maternal benefit–risk assessment in lactation

In contemporary practice, pirenzepine has largely been supplanted by alternative anti‑ulcer agents (such as proton pump inhibitors and H2‑receptor antagonists) that are better characterised in breastfeeding and generally regarded as compatible at usual doses. Given the limited therapeutic necessity of pirenzepine, the existence of better‑studied alternatives, and the potential for serious anticholinergic toxicity in infants, the maternal benefit–risk balance during lactation is unfavourable for routine use.gpnotebook+3

Duration–risk considerations in breastfeeding

Because of its half‑life and likely low but non‑negligible passage into milk, repeated dosing can lead to sustained low‑level infant exposure rather than transient peaks. Short‑term, single‑dose exposure would theoretically pose less risk than prolonged courses, but even brief therapy cannot be considered safe in high‑risk infants and should only be contemplated if no safer alternative exists and under close pediatric surveillance.psychopharmacologyinstitute+2

Pregnancy considerations (context)

Product information discourages the use of pirenzepine during pregnancy, generally citing lack of adequate data rather than clear teratogenic signals, and it is assigned to pregnancy risk category C in older FDA‑style classifications. When therapy for peptic ulcer disease or dyspepsia is required in pregnancy, other agents with more reassuring fetal safety data are preferred.file+3

Overall lactation safety classification

Despite limited quantitative data, pirenzepine’s anticholinergic mechanism, documented transfer into breast milk, and potential for severe cardiac and autonomic effects in neonates justify classification as toxicologically inappropriate during breastfeeding. Accordingly, in a toxico‑lactological framework, pirenzepine is best placed in the highest risk category (e.g. toxicological lactation category IV: completely unsuitable for use during lactation), warranting active avoidance in breastfeeding mothers whenever possible.medsafe+2

Practical recommendations for clinical use

In breastfeeding women with peptic ulcer disease or antipsychotic‑induced hypersalivation, clinicians should prioritise non‑pharmacological measures and alternative medications with established lactation safety over pirenzepine. If a patient is already receiving pirenzepine and breastfeeding, a planned switch to a safer, well‑studied agent—combined with careful infant monitoring for anticholinergic signs (poor feeding, constipation, urinary retention, tachycardia, lethargy)—is advisable, and abrupt cessation of breastfeeding may be considered in high‑risk situations after individualised risk–benefit discussion.gpnotebook+3