Metronidazole
| Evidence Level: L5 | Predicted Indications: 10 |
Table of Contents
Metronidazole: From Anaerobic Bacterial and Protozoal Infections to Pneumocystosis
One-Sentence Summary
Metronidazole is a nitroimidazole antimicrobial originally used for anaerobic bacterial infections, giardiasis, bacterial vaginosis and rosacea. The TxGNN model predicts it may be effective for pneumocystosis (score 99.99%), but no clinical trials are registered and none of the 10 retrieved publications shows metronidazole working against Pneumocystis. This top-ranked prediction therefore rests on model output alone, and other lower-ranked predictions (such as cap polyposis) have more plausible support.
Quick Overview
| Item | Content |
|---|---|
| Original Indication | Anaerobic bacterial infections, giardiasis, bacterial vaginosis, rosacea, peritonitis, intracranial abscess (the Singapore licence records contain no indication text, so these come from the knowledge graph) |
| Predicted New Indication | Pneumocystosis |
| TxGNN Prediction Score | 99.99% |
| Evidence Level | L5 |
| Singapore Market Status | ✓ Marketed |
| Number of Registrations | 11 |
| Recommended Decision | Hold |
Why is This Prediction Reasonable?
Currently, detailed mechanism of action data is not available. Based on known information, metronidazole is a nitroimidazole antimicrobial. Its efficacy in anaerobic bacterial and protozoal infections is established, and it is also used topically for rosacea. It is activated by nitroreduction in anaerobic organisms.
For pneumocystosis, this link is weak. Pneumocystis is a fungus that lacks the nitroreduction pathway metronidazole depends on, so no plausible mechanism is evident. The high model score appears to reflect general anti-infective associations. The retrieved literature consists of general antiparasitic reviews and HIV opportunistic infection case reports. In those reports, metronidazole was given for a co-existing infection such as amoebiasis, not for Pneumocystis.
Among the other predictions, cap polyposis (rank 9) has the most plausible rationale. It is linked to gut dysbiosis, and case reports describe remission after metronidazole-containing regimens. Ulcerative proctosigmoiditis (rank 3) has indirect support from metronidazole's use in other inflammatory bowel conditions. These are noted as follow-up research questions.
Clinical Trial Evidence
Currently no related clinical trials registered.
Literature Evidence
| PMID | Year | Type | Journal | Key Findings |
|---|---|---|---|---|
| 1545596 | 1992 | Review | Mayo Clinic Proceedings | General review of antiparasitic agents; no demonstrated metronidazole efficacy against Pneumocystis |
| 7355683 | 1980 | Review | American Family Physician | Lists metronidazole for amoebiasis and trichomoniasis; trimethoprim-sulfamethoxazole is listed for Pneumocystis pneumonia |
| 1782741 | 1991 | Review | Clinical Pharmacokinetics | Pharmacokinetic basis of antiprotozoal therapy, including in immunocompromised patients |
| 2996829 | 1985 | Review | Clinical Pharmacy | Treatment of infectious complications of AIDS; Pneumocystis pneumonia is the most common |
| 26518395 | 2015 | Review | Topics in Antiviral Medicine | Update on HIV-related opportunistic infections; no metronidazole data for Pneumocystis |
| 6771863 | 1980 | Review | Reviews of Infectious Diseases | Critique of antimicrobial prophylaxis trials; not specific to Pneumocystis |
| 6282154 | 1982 | Case report | American Review of Respiratory Disease | Pneumocystis and cytomegalovirus pneumonia in a patient previously given metronidazole and tetracycline for diarrhoea |
| 2338506 | 1990 | Case report | Kansenshogaku Zasshi | Two AIDS patients; metronidazole treated amoebic dysentery and liver abscess, not Pneumocystis |
| 16496064 | 2005 | Case report | J Formos Med Assoc | AIDS patient with colon perforation from CMV and amoebic colitis |
| 42178576 | 2026 | Case report | J Med Case Reports | Streptococcus intermedius cerebellar abscess in sarcoidosis; unrelated to Pneumocystis |
Singapore Market Information
| Authorization Number | Product Name | Dosage Form | Approved Indication |
|---|---|---|---|
| SIN10509P | AXCEL METRONIDAZOLE-200 TABLETS 200 mg | Tablet | Not recorded |
| SIN03741P | AA PHARMA METRONIDAZOLE TABLET 250 mg | Tablet | Not recorded |
| SIN01260P | METRONIDAZOLE INTRAVENOUS INFUSION 500 mg/100 ml | Injection | Not recorded |
| SIN11737P | METRONIDAZOLE FRESENIUS SOLUTION FOR INFUSION 500 mg/100 ml | Injection | Not recorded |
| SIN11198P | ROZEX CREAM 0.75% | Cream | Not recorded |
Eleven valid single-ingredient licences are registered in total. The others include further oral tablets, a topical gel and two vaginal suppository products. Available routes are oral, injectable, topical and vaginal.
Safety Considerations
Package insert warnings and contraindications were not available for this report; please refer to the package insert for safety information.
- Contraindication-related conditions (knowledge graph, not label text): Caution is flagged for liver failure and liver disease, epilepsy and other brain disease, kidney disease, blood disorders (neutropenia, leukopenia, agranulocytosis, coagulation disease), peripheral neuropathy and other peripheral nervous system disease, optic nerve and visual pathway disease, congestive heart failure, diabetes and diabetic ketoacidosis, gout, gallbladder disease, non-infectious meningitis, dermatitis, and substance abuse/dependence.
- Drug Interactions: 100 interactions were found. The most notable is ethanol (Major). Moderate interactions include paclitaxel, adalimumab, trastuzumab emtansine, ethinylestradiol, estradiol, amiodarone, celecoxib, butalbital, amobarbital and loperamide. The remainder shown are minor, such as tramadol, famotidine and amitriptyline.
Conclusion and Next Steps
Decision: Hold
Rationale: The pneumocystosis prediction is purely computational (L5). There are no clinical trials, and the retrieved literature does not support metronidazole activity against Pneumocystis. Pneumocystis lacks the pathway metronidazole needs, and standard therapy is trimethoprim-sulfamethoxazole-based. Cap polyposis, ulcerative proctosigmoiditis, myiasis (adjunctive use) and vulvar ulceration are better candidates for further exploration, but each is still only a research question at L4.
To proceed, the following is needed:
- Detailed mechanism of action data (MOA)
- Package insert warnings and contraindications from the HSA website, which is a blocking gap for safety screening
- For cap polyposis, a structured review of case reports and, if justified, a small controlled study
- Re-evaluation of the model's predictions after removing associations driven by general anti-infective similarity
Disclaimer
This content is for research purposes only and does not constitute medical advice. Clinical validation is required before any clinical application.