Cimetidine

Evidence Level: L5

Predicted Indications: 10

Cimetidine
Cimetidine: From Peptic Ulcer and Acid-Related Disorders to Smouldering Systemic Mastocytosis

## Pharmacist Assessment Report

One-Sentence Summary

Cimetidine is a histamine H2-receptor antagonist, originally used for gastric and duodenal ulcers, reflux disease and gastric hypersecretory states. The TxGNN model predicts it may be useful for Smouldering Systemic Mastocytosis, but no clinical trials and no publications specific to this condition were found in the data compiled for this report, so the prediction rests on model output alone.

Quick Overview

Item	Content
Original Indication	Gastric ulcer, duodenal ulcer, gastroesophageal reflux disease, esophagitis, dyspepsia, Zollinger-Ellison syndrome (the Singapore licence records contain no indication text; the indications listed here come from the knowledge graph)
Predicted New Indication	Smouldering systemic mastocytosis
TxGNN Prediction Score	99.80%
Evidence Level	L5
Singapore Market Status	✓ Marketed
Number of Registrations	8
Recommended Decision	Hold

Why is This Prediction Reasonable?

Detailed mechanism-of-action data was not available in the data compiled for this report. Cimetidine is a well-known H2-receptor antagonist: it blocks histamine at the H2 receptors on gastric parietal cells and so reduces acid secretion.

Systemic mastocytosis is already among cimetidine's knowledge-graph indications, where the benefit is control of histamine-driven gastric hypersecretion. The high score for the smouldering subtype most likely reflects this overlap within the mastocytosis disease family. Any benefit would be symptomatic (acid- and histamine-mediated symptoms). Cimetidine would not be expected to act on the underlying clonal mast cell burden.

Clinical Trial Evidence

Currently no related clinical trials registered.

Literature Evidence

Currently no related literature available for smouldering systemic mastocytosis.

For context, the other predicted indications are all L4 or L5 and carry the following literature:

Predicted Indication	Score	Evidence Level	Supplied Literature	Assessment
Active peptic ulcer disease	99.79%	L4	18 publications, mostly reviews of other agents; one 1981 double-blind trial (PMID 7034155) showed 67% healing at 3 weeks with cimetidine vs placebo	Already an approved indication, so not true repurposing
Peptic ulcer perforation	99.77%	L4	Mostly case reports of perforation occurring during cimetidine therapy	Safety signal or treatment failure, not benefit
Gastrojejunal ulcer	99.77%	L4	General peptic ulcer reviews and commentary	Indirect evidence only
Lymphoadenopathic mastocytosis with eosinophilia	99.76%	L5	None	Unsupported by clinical evidence
Duodenogastric reflux	99.49%	L4	Physiological studies of gastric secretion and bile acids (PMID 4018640)	Cimetidine does not address bile reflux
Duodenal obstruction	99.44%	L4	A 1978 report of response in ulcer-related gastric outlet obstruction (PMID 361048)	Secondary symptomatic effect only
Acne	99.33%	L4	Reviews, including a 1982 dermatology overview of H2 antagonists (PMID 6130053)	Weak anti-androgenic link; research question only
Abnormality of glucagon secretion	99.14%	L5	One Meckel's diverticulum imaging study (PMID 6088239)	Not relevant
Gastroduodenitis	98.89%	L4	Mostly reviews of other agents	Largely label extension

Singapore Market Information

Authorization Number	Product Name	Dosage Form	Approved Indication
SIN08029P	XEPAMET TABLETS 200 mg	Film-coated tablet	Not recorded
SIN09571P	CIMETIDINE TABLET 200 mg	Tablet	Not recorded
SIN08030P	XEPAMET TABLETS 400 mg	Film-coated tablet	Not recorded
SIN08908P	CIMETIDINE 400 FILM-COATED TABLET 400 mg	Film-coated tablet	Not recorded
SIN07835P	CIMETIDINE TABLETS 200 mg	Film-coated tablet	Not recorded

Eight valid single-ingredient licences are registered in total; the five above are shown. All are oral tablets and none are cancelled.

Safety Considerations

Knowledge-graph contraindication signals (from the knowledge graph, not from label text): liver disease, gallbladder disease, impaired renal function, and gastric cancer or neoplasm (including diffuse gastric adenocarcinoma, linitis plastica and gastric carcinoma).
Drug Interactions: 100 interactions were identified. Examples among those listed:
- Moderate: paclitaxel, fentanyl, acalabrutinib, lidocaine, acebutolol, dihydrocodeine, codeine, tramadol, nifedipine, alfentanil.
- Minor: dolutegravir, zidovudine, acetaminophen, ketorolac, ibuprofen, ethinylestradiol, albendazole, ethanol, alendronic acid, cholecalciferol.
Package insert warnings and contraindications were not available. Please refer to the package insert for full safety information.

Conclusion and Next Steps

Decision: Hold

Rationale: The smouldering systemic mastocytosis prediction has a high model score but no trials or literature behind it (L5). Even if the prediction holds, the likely benefit is symptom control only. Most other predicted indications are existing approved uses, or are unsupported or contradicted by the supplied evidence.

To proceed, the following is needed:

Package insert warnings and contraindications from the HSA website, which is currently a blocking gap for safety screening
Mechanism-of-action data from DrugBank
A targeted literature and trial search on H2 antagonists in smouldering systemic mastocytosis, including a comparison with standard antihistamine and mast cell-directed therapy
A review of the contraindication signals (liver, renal, gallbladder disease) against the target population
Review of the interaction list for drugs likely to be co-prescribed in mastocytosis patients
Disclaimer

This content is for research purposes only and does not constitute medical advice. Clinical validation is required before any clinical application.