Metronidazol
Metronidazole
2-(2-methyl-5-nitro-1H-imidazol-1-yl)ethanol; Metronidazole benzoate
También conocido como: Flagyl · Metrobactin · Stomorgyl · Metronidazole benzoate · Bayer-5360 · metronidazolum · SC-32642 · NSC-50364 · RP-8823 · SC-10295
Revisado por el equipo veterinario de VetSheetActualizado 5 abr 2026Referencia veterinaria basada en la evidencia
Evidencia posológica v13 auditada
Evidencia estructurada para el cálculoAnaerobic infections (extra-label) — less severe anaerobic infections
- q8-12h
NA
Contexto clínico obligatorio (6)
- 1. Dosages are for metronidazole base unless otherwise noted. If metronidazole benzoate is being used, dosages should be adjusted unless provided by pharmacy as “mg/mL of the base.”
- One mg of metronidazole base = 1.6 mg of metronidazole benzoate. For example, if the calculated metronidazole dose is 200 mg (of the base), the corresponding dose using metronidazole benzoate would be 320 mg (metronidazole benzoate).
- 2. Because of the drug’s extreme bitterness, using a flavored, compounded metronidazole benzoate or putting quartered tablets in an empty gelatin capsule may be considered.
- Anaerobic infections (extra-label):
- ■ Give this medication with food.
- Metronidazole tablets and solution for injection should be stored at temperatures less than 30°C (86°F) and protected from light. The shelf life of divided tablets is 3 days. 5
Hepatic encephalopathy (extra-label)
- q8-12h
NA
Contexto clínico obligatorio (5)
- 1. Dosages are for metronidazole base unless otherwise noted. If metronidazole benzoate is being used, dosages should be adjusted unless provided by pharmacy as “mg/mL of the base.”
- One mg of metronidazole base = 1.6 mg of metronidazole benzoate. For example, if the calculated metronidazole dose is 200 mg (of the base), the corresponding dose using metronidazole benzoate would be 320 mg (metronidazole benzoate).
- 2. Because of the drug’s extreme bitterness, using a flavored, compounded metronidazole benzoate or putting quartered tablets in an empty gelatin capsule may be considered.
- ■ Give this medication with food.
- Metronidazole tablets and solution for injection should be stored at temperatures less than 30°C (86°F) and protected from light. The shelf life of divided tablets is 3 days. 5
Las dosis son una referencia clínica para profesionales veterinarios autorizados. Confirme siempre con el prospecto actual y cada paciente individual.
Resumen
El metronidazol es un agente antibacteriano y antiprotozoario sintético del grupo de los nitroimidazoles, ampliamente utilizado en medicina veterinaria.
Aplicaciones clínicas clave:
- Antiprotozoario: Altamente eficaz contra Giardia, Trichomonas, Entamoeba histolytica y Balantidium coli.
- Antibacteriano anaerobio: Excelente eficacia contra anaerobios obligados (p. ej., Bacteroides, Clostridium, Fusobacterium). Se utiliza frecuentemente para infecciones anaerobias entéricas y sistémicas, incluyendo sepsis, peritonitis y heridas por mordedura profundas.
- Modulador gastrointestinal: Utilizado frecuentemente en el manejo de la enfermedad inflamatoria intestinal (EII) y colitis crónica. Perla clínica: Más allá de sus propiedades antimicrobianas, se cree que el metronidazol tiene efectos inmunomoduladores y antiinflamatorios locales en el tracto gastrointestinal, específicamente mediante la inhibición de la inmunidad mediada por células.
Consideraciones importantes:
- Estrictamente prohibido por la FDA para su uso en animales destinados al consumo humano.
- Es conocido por su sabor extremadamente amargo y metálico, que puede causar hipersalivación profunda y aversión a la medicación, especialmente en gatos. El benzoato de metronidazol compuesto suele preferirse para pacientes felinos, ya que es menos soluble en la saliva y, por lo tanto, menos amargo.
Mecanismo de acción
Metronidazole is a concentration-dependent bactericidal agent.
Mechanism Pathway:
- Entry: The drug enters the cell of the organism via passive diffusion.
- Activation: In obligate anaerobes and certain protozoa, the nitro group of metronidazole is reduced by electron-transport proteins (such as ferredoxin).
- DNA Disruption: This reduction process creates highly reactive, short-lived cytotoxic intermediate compounds (free radicals) → These radicals bind to and disrupt DNA and nucleic acid synthesis → leading to rapid cell death.
Because aerobic bacteria lack the specific electron-transport proteins required to reduce and activate the drug, metronidazole is virtually inactive against obligate aerobes.
Seguridad y advertencias
Contraindicaciones
- Hypersensitivity to metronidazole or other nitroimidazole derivatives
- Food-producing animals (FDA prohibited)
- Pregnancy (potential teratogen, especially in early pregnancy)
- Severe hepatic disease (requires dose reduction)
Efectos adversos
- Neurologic disorders (ataxia, nystagmus, seizures, head-tilt)
- Lethargy and weakness
- Neutropenia
- Hepatotoxicity
- Hematuria
- Anorexia, nausea, vomiting, and diarrhea
- Hypersalivation (especially in cats due to bitter taste)
- CNS toxicity (nystagmus, ataxia, knuckling, head tilt, seizures)
- Haematuria
- Excessive salivation/foaming (especially in cats)
- Impaired sense of smell (reported in explosive detection dogs)
Precauciones
Neurotoxicity Warning: In dogs, total daily doses should not exceed 65 mg/kg/day to minimize the risk of central vestibular and cerebellar toxicity. Toxicity can occur with acute high doses or chronic moderate-to-high dose therapy.
- Hepatic Impairment: Use with caution in animals with hepatic dysfunction. Consider reducing the dose to 25-50% of the usual dose in significant liver impairment.
- Pregnancy: Potential teratogen. Avoid use during pregnancy, particularly during the first 3 weeks of gestation, unless benefits clearly outweigh risks.
- Nursing: Consider alternative therapy or switching to milk replacer due to potential tumorigenicity.
- Debilitated Patients: Use with extreme caution in severely debilitated animals.
Interacciones farmacológicas
May induce a disulfiram-like reaction (nausea, vomiting, cramps).
May decrease the metabolism of metronidazole, increasing the likelihood of dose-related side effects.
May increase the metabolism of metronidazole, thereby decreasing blood levels.
May increase the metabolism of metronidazole, thereby decreasing blood levels.
May prolong the prothrombin time (PT). Avoid concurrent use or intensify monitoring.
Should not be used concurrently with Spiramycin (in combination products) as the combination may be antagonistic.
Monitorización
- Clinical efficacy (resolution of diarrhea, negative fecal tests)
- Adverse effects (especially neurologic signs like ataxia or nystagmus)
- Neurological signs (for early detection of CNS toxicity)
- Liver function tests (ALT, AST, Bilirubin) in patients with pre-existing hepatic disease
- Complete Blood Count (for neutropenia)
Farmacocinética
Vida media
Absorción
Relatively well absorbed after oral administration. Oral bioavailability in dogs is high (50-100%) and enhanced with food. In cats, bioavailability averages ~65%. In horses, oral bioavailability averages ~80% (decreased by 50% if given rectally).
Distribución
Highly lipophilic and widely distributed to most body tissues and fluids, including bone, abscesses, the CNS, and seminal fluid. Less than 20% bound to plasma proteins.
Metabolismo
Primarily metabolized in the liver via several pathways, including glucuronidation.
Eliminación
Both metabolites and unchanged drug are eliminated in the urine and feces.
Sobredosis
Signs of intoxication in dogs and cats are primarily neurologic and include:
- Anorexia and/or vomiting
- Depression
- Mydriasis (dilated pupils)
- Nystagmus (rapid eye flicking, very common in dogs)
- Ataxia (stumbling, uncoordinated gait)
- Head-tilt, proprioceptive deficits, joint knuckling
- Tremors, seizures, rigidity, and stiffness
These effects may be seen with acute massive overdoses, or more commonly with chronic therapy at doses >60 mg/kg/day (though sometimes seen at 'recommended' doses like 30 mg/kg/day).
Treatment:
- Discontinue metronidazole immediately. Most dogs with mild to moderate signs improve rapidly within 1-2 days of stopping the drug.
- Diazepam has been used successfully to rapidly decrease the CNS effects associated with metronidazole toxicity.
- For acute massive ingestions, standard decontamination protocols (emesis, activated charcoal) apply, but use extreme caution before inducing vomiting if the patient is already showing CNS signs, due to aspiration risk.
Productos disponibles
Formulaciones
- Oral capsules
- Extended-release oral tablets
- Injection (IV)
- Compounded oral suspensions (often using metronidazole benzoate)
- 5 mg/ml i.v. infusion
- 250 mg tablet
- 500 mg tablet
- 25 mg metronidazole + 46.9 mg spiramycin tablet (Stomorgyl 2)
- 125 mg metronidazole + 234.4 mg spiramycin tablet (Stomorgyl 10)
- 250 mg metronidazole + 469 mg spiramycin tablet (Stomorgyl 20)
- 40 mg/ml oral solution
Veterinario
- None (Prohibited for use in food animals by the FDA)
- Metrobactin 250 mg, 500 mg tablets
- Stomorgyl 2, 10, 20 tablets (combination with spiramycin)
Etiquetado para humanos
- Metronidazole Oral Tablets: 250 mg & 500 mg (Flagyl, generic)
- Metronidazole Oral Capsules: 375 mg (Flagyl 375, generic)
- Metronidazole Extended-Release Oral Tablets: 750 mg (Flagyl ER)
- Metronidazole Injection: 5 mg/mL in 100 mL vials
- Bismuth Subsalicylate, Metronidazole & Tetracycline HCl Combination (Helidac)
- Flagyl 200 mg, 400 mg tablets
- Metronidazole 5 mg/ml IV infusion
Estado regulador
POM-V classification. Prohibited for use in food-producing animals.
POM-V classification.
Sin datos reguladores para: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Almacenamiento y estabilidad
Tablets and HCl powder for injection should be stored at temperatures less than 30°C and protected from light. The injection should be protected from light and freezing and stored at room temperature. Compounded metronidazole benzoate suspensions can be stable for up to 90 days or longer depending on the specific vehicle used.
Información para el cliente
Guía importante para los propietarios de mascotas:
- Sabor extremadamente amargo: Las tabletas de metronidazol tienen un sabor terrible para los animales. No triture las tabletas a menos que sea estrictamente necesario, ya que el sabor amargo hará que su mascota (especialmente los gatos) babee excesivamente o rechace la comida. Si tiene dificultades para administrar el medicamento, consulte a su veterinario sobre una versión líquida compuesta (benzoato de metronidazol), que oculta el sabor mucho mejor.
- Administrar con comida: Dar este medicamento junto con una comida puede ayudar a mejorar su absorción y reducir el malestar estomacal.
- Vigile los signos neurológicos: Contacte a su veterinario inmediatamente si su mascota muestra cualquier signo de toxicidad neurológica. Esté atento a: tropiezos o caminar como si estuviera "ebrio" (ataxia), movimientos oculares rápidos de un lado a otro (nistagmo), inclinación de la cabeza, letargo extremo, temblores o convulsiones.
- Complete el tratamiento: Incluso si la diarrea o los síntomas de su mascota mejoran, termine todo el tratamiento prescrito para asegurar que la infección o el parásito se eliminen por completo.
La referencia de medicamentos de VetSheet está destinada a profesionales veterinarios autorizados como ayuda para la toma de decisiones clínicas, no como sustituto del criterio profesional ni del prospecto actual del fabricante.