Metronidazole + Nystatin

Hypersensitivity to metronidazole, nystatin, or imidazoles. Combined treatment with oral metronidazole in cases of active neurological disorders or in patients with history of blood dyscrasia, hypothyroidism, or hypoadrenalism (unless benefits outweigh possible risk in the opinion of the physician).

Patient with Cockayne syndrome; hepatic encephalopathy, history of liver injury associated with metronidazole; active or chronic peripheral and central nervous system diseases. Sexual partners should be treated concomitantly with oral metronidazole when there is evidence of trichomonal infestation. Avoid use with vaginal injection, menstrual tampons, and soaps with an acid pH during treatment, as they may promote fungal replication. May reduce the effectiveness of condoms or diaphragms; concurrent use is not recommended. Severe hepatic impairment. Use during the 1st trimester of pregnancy is not recommended, and the applicator must not be used after the 7th month of pregnancy. Avoid use during breastfeeding.

Significant: Local irritation or sensitivity, suicidal ideation with or without depression, darker urine. Metronidazole: Peripheral or central neuropathy; severe cutaneous adverse reactions (SCARs), including acute generalised exanthematous pustulosis (AGEP), Stevens-Johnson syndrome (SJS), drug reaction with eosinophilia and systemic syndrome (DRESS), toxic epidermal necrolysis (TEN); fungal or bacterial superinfection, including Clostridioides difficile-associated diarrhoea, pseudomembranous colitis (prolonged use).
Blood and lymphatic system disorders: Transient eosinophilia, neutropenia, thrombocytopenia, agranulocytosis.
Eye disorders: Decreased visual acuity, diplopia, myopia, vision colour changes, optic neuritis or neuropathy.
Gastrointestinal disorders: Bitter or metallic taste, coated tongue, nausea, vomiting, diarrhoea, dry mouth.
General disorders and administration site conditions: Fatigue.
Musculoskeletal and connective tissue disorders: Arthralgia (including ankles, wrists), joint swelling (including ankles, wrists).
Nervous system disorders: Dizziness, headache.
Reproductive system and breast disorders: Vaginal discomfort (granular sensation), vulvovaginal burning sensation.
Skin and subcutaneous tissue disorders: Pruritus, rash, urticaria.
Potentially Fatal: Metronidazole: Severe hepatotoxicity or acute hepatic failure (in patients with Cockayne syndrome).

This drug may cause dizziness, vertigo, confusion, hallucinations, convulsions or eye disorders, if affected, do not drive or operate machinery. Discontinue treatment if local irritation or sensitisation occurs. This drug may decrease the effectiveness of condoms or diaphragms; other forms of birth control methods must be used during therapy.

Perform culture and susceptibility tests; consult local institutional recommendations before treatment initiation due to antibiotic resistance risks. Monitor LFTs before treatment initiation, during therapy, and after treatment until liver function is within the normal range or until baseline values are reached (in patients with Cockayne syndrome). Obtain total and differential leucocyte counts before and after treatment, particularly if a second course of metronidazole therapy is needed. Assess mental status, neurological symptoms, and any dermatologic reactions.

Metronidazole: Increased risk of CNS toxicity (e.g. psychosis) with disulfiram. May potentiate the effects of anticoagulants (e.g. warfarin), leading to prolongation of the prothrombin time. May increase serum levels of lithium, busulfan, phenytoin and ciclosporin. May reduce the clearance of fluorouracil, potentially increasing toxicity. Phenytoin or phenobarbital may decrease the serum levels of metronidazole. May slightly potentiate the neuromuscular blocking effects of vecuronium.

Metronidazole: May cause disulfiram-like reactions with alcohol.

Metronidazole: May interfere with AST, ALT, triglycerides, glucose, and LDH tests, potentially leading to false negative or abnormally low test results.

Description:
Overview: Metronidazole is a nitroimidazole derivative that is active against anaerobic bacteria and protozoa.
Nystatin, a polyene antibiotic, is an antifungal agent that is active against a variety of yeasts and yeast-like fungi.
Mechanism of Action: The exact mechanism of metronidazole has not been fully established; however, after diffusing into susceptible organisms, it is suggested to interact with DNA, causing loss of the helical DNA structure and strand breakage, which results in inhibition of protein synthesis and subsequent cell death.
Nystatin binds to sterols in the fungal cell membrane, disrupting cell wall permeability, thereby allowing the leakage of intracellular components.
Pharmacodynamics: Resistance to metronidazole may develop from decreased nitroreductase activity and/or poor cell penetration. Cross-resistance may also occur to other nitroimidazoles (e.g. tinidazole). Primary resistance to nystatin is rare, but Candida resistant to nystatin may be cross-resistant to other polyene antifungals (e.g. amphotericin B, natamycin).
Pharmacokinetics:
Absorption: Metronidazole: May be absorbed systematically after vaginal administration. Bioavailability: 20-25%.
Distribution: Metronidazole: Widely distributed in most body tissues and fluids, including bone, cerebral abscesses, CSF, bile, liver and liver abscesses, saliva, seminal fluid, and vaginal secretions. Crosses the placenta and enters breast milk. Plasma protein binding: <20%.
Metabolism: Metronidazole: Metabolised in the liver via side chain oxidation and glucuronide formation into metabolites, including 1-(2-hydroxyethyl)-2-hydroxymethyl-5-nitroimidazole (hydroxy metabolite) and 2-methyl-5-nitroimidazole-lacetic acid (acid metabolite).
Excretion: Metronidazole: Mainly via urine (60-80% as unchanged drug and metabolites; approx 20% of total as unchanged drug); faeces (6-15%). Elimination half-life: Approx 8 hours.

Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 4173, Metronidazole. https://pubchem.ncbi.nlm.nih.gov/compound/Metronidazole. Accessed Feb. 24, 2026.

Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 6433272, Nystatin [USP:INN:BAN:JAN]. https://pubchem.ncbi.nlm.nih.gov/compound/Nystatin-_USP_INN_BAN_JAN. Accessed Feb. 24, 2026.

Store between 15-25°C. Protect from light.

Preparations for Vaginal Conditions

G01AA51 - nystatin, combinations ; Belongs to the class of antibiotics. Used in the treatment of gynecological infections.

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