Acetato de megestrol
Megestrol Acetate
17-alpha-acetoxy-6-dehydro-6-methylprogesterone
También conocido como: Ovaban · Megace · Ovarid · BDH-1298 · compound 5071 · megestroli acetas · NSC-71423 · SC-10363 · Acestrol · Borea · Endace · Gynodal · Maygace · Megastrol · Megefren · Megestat · Megestil · Megestin · Megostat · Meltonar · Meprogest · Mestrel · Niagestine · Prazoken · Varigestrol
Revisado por el equipo veterinario de VetSheetActualizado 5 abr 2026Referencia veterinaria basada en la evidencia
Las dosis son una referencia clínica para profesionales veterinarios autorizados. Confirme siempre con el prospecto actual y cada paciente individual.
Dosis por especie
🌎 NA — North America🌍 EU — Europe
Perros
| Indicación | Dosis | Vía | Frecuencia | Duración | Región |
|---|---|---|---|---|---|
| To halt cycle in proestrus | 2.2 mg/kg once daily for 8 days starting during the first 3 days of proestrus. May be prolonged with 2.2 mg/kg/day for 4 days, then 0.55 mg/kg/day for 16-20 days. | PO | q24h | 8-24 days | 🌎 NA |
| To postpone an anticipated cycle | 0.55 mg/kg/day for 32 days, beginning at least 7 days prior to proestrus | PO | q24h | 32 days | 🌎 NA |
| To delay an anticipated heat during anestrus | 0.55 mg/kg PO for 32 days initiated 7 days prior to proestrus. | PO | q24h | 32 days | 🌎 NA |
| Estrus suppression (general) | 2 mg/kg PO once daily for 8 consecutive days | PO | q24h | 8 days | 🌎 NA |
| Temporary estrus postponement (general) | 0.5 mg/kg PO once daily in late anestrus | PO | q24h | Variable | 🌎 NA |
| Benign prostatic hypertrophy | 0.5 mg/kg PO daily for 4-8 weeks | PO | q24h | 4-8 weeks | 🌎 NA |
| Benign prostatic hypertrophy | 0.55 mg/kg PO daily | PO | q24h | Variable | 🌎 NA |
| Benign prostatic hypertrophy | 0.1-0.5 mg/kg per day for 3-8 weeks | PO | q24h | 3-8 weeks | 🌎 NA |
| Pseudocyesis (false pregnancy) | 0.5 mg/kg PO once daily for 8 days | PO | q24h | 8 days | 🌎 NA |
| To prevent vaginal hyperplasia development | 2.2 mg/kg PO for 7 days early in proestrus | PO | q24h | 7 days | 🌎 NA |
| Treatment of severe galactorrhea | 0.55 mg/kg PO once daily for 7 days | PO | q24h | 7 days | 🌎 NA |
| Adjunctive treatment of aggressive or unacceptable masculine behavior | 1.1-2.2 mg/kg PO once daily for 2 weeks, then 0.5-1.1 mg/kg once daily for 2 weeks. | PO | q24h | 4 weeks | 🌎 NA |
- To halt cycle in proestrus: Bitch must be controlled until behavioral signs of estrus disappear.
- To delay an anticipated heat during anestrus: Recommend doing vaginal cytology prior to therapy. Do not repeat therapy more often than once every 6 months.
- Benign prostatic hypertrophy: Best used to maintain breeding potential for short time prior to castration; use with caution.
- Adjunctive treatment of aggressive or unacceptable masculine behavior: Should be used with behavior modification.
Gatos
| Indicación | Dosis | Vía | Frecuencia | Duración | Región |
|---|---|---|---|---|---|
| Suppression of estrus (in anestrus) | 5 mg/cat PO every 2 weeks or 2.5 mg/cat per week (better if divided into 2 doses given every 3.5 days) | PO | q7-14d | Variable | 🌎 NA |
| Suppression of estrus (in proestrus) | 5 mg/cat per day for 4 days, then 5 mg PO every 2 weeks. | PO | q24h then q14d | Variable | 🌎 NA |
| Suppression of estrus (behavioral estrus) | 5 mg/day PO until estrus stops (generally within 3-5 days), then 2.5-5 mg PO once weekly for 10 weeks | PO | q24h then q7d | 10+ weeks | 🌎 NA |
| Postponement of estrus (started during diestrus) | 2.5 mg PO daily for 8 weeks | PO | q24h | 8 weeks | 🌎 NA |
| Postponement of estrus (started during anestrus) | 2.5 mg PO once weekly for up to 18 months. | PO | q7d | Up to 18 months | 🌎 NA |
| Prevention of estrus | 5 mg daily PO for 3 days as soon as behavioral signs of estrus are seen | PO | q24h | 3 days | 🌎 NA |
| Idiopathic feline miliary dermatitis | 2.5-5 mg once every other day, followed by weekly maintenance dosages. | PO | q48h then q7d | Variable | 🌎 NA |
| Appetite stimulant | 0.25-0.5 mg/kg q24h for 3-5 days, then q48-72h | PO | q24h then q48-72h | Variable | 🌎 NA |
| Alternative treatment for immune-mediated skin diseases | 2.5-5 mg PO once daily for 10 days, then every other day | PO | q24h then q48h | Variable | 🌎 NA |
| Adjunctive therapy of eosinophilic granulomas | 0.5 mg/kg PO once daily for 2 weeks, then twice weekly as needed | PO | q24h then twice weekly | Variable | 🌎 NA |
| Eosinophilic ulcers | 5-10 mg PO every other day for 10-14 doses, then every 2 weeks as needed | PO | q48h then q14d | Variable | 🌎 NA |
| Feline atopy ('last ditch' alternative) | 2.5-5 mg per cat PO every 48 hours for 1-3 weeks. This dose is then used once weekly. | PO | q48h then q7d | Variable | 🌎 NA |
| Feline plasma cell gingivitis | 2.5 mg PO once daily for 10 days, then once every other day for 5 treatments, then as needed | PO | q24h then q48h | Variable | 🌎 NA |
| Feline endocrine alopecia (FEA) | 5 mg PO every second to third day initially, then 2.5 mg PO once to twice weekly | PO | q48-72h then 1-2x weekly | Variable | 🌎 NA |
| Feline psychogenic alopecia and dermatitis | 2.5-5 mg every other day initially, then taper to the lowest maintenance dosage possible, given weekly as needed | PO | q48h then q7d | Variable | 🌎 NA |
| Persistent hematuria and urethritis in a non-obstructed cat | 2.5-5 mg PO once daily to every other day (with prednisone: 2.5-5 mg PO daily) | PO | q24-48h | Variable | 🌎 NA |
| Urine marking, intraspecies aggression, anxiety | 2 mg/kg/day for 5 days, then 1 mg/kg/day for 5 days, then 0.5 mg/kg/day for 5 days | PO | q24h | 15 days | 🌎 NA |
| To reduce marking in neutered male cats | 2.5-10 mg (total dose) per cat PO once daily for one week, then reduce to once or twice weekly. | PO | q24h then 1-2x weekly | Variable | 🌎 NA |
| Urine marking, intraspecies aggression, anxiety | 5 mg per cat once daily for 2 weeks, then wean to lowest effective maintenance dose. | PO | q24h | Variable | 🌎 NA |
- Postponement of estrus (started during anestrus): Recommend allowing cat to have a cycle (unmedicated) before beginning another treatment cycle.
- Prevention of estrus: Next estrus period will occur in approximately 4 weeks.
- Idiopathic feline miliary dermatitis: Reserve use for severe cases; explain risks to owner and do not exceed 2.5 mg per week during maintenance phase.
- Eosinophilic ulcers: Alone or in combination with methylprednisolone acetate.
- Feline endocrine alopecia (FEA): Secondary therapy (thyroid hormone replacement first choice).
- Persistent hematuria and urethritis in a non-obstructed cat: Adjunctive therapy.
- To reduce marking in neutered male cats: When all other drugs have been unsuccessful.
- Urine marking, intraspecies aggression, anxiety: Has poor efficacy in neutered males (50%) and spayed females (10%); many potential adverse effects.
Las dosis son una referencia clínica para profesionales veterinarios autorizados. Confirme siempre con el prospecto actual y cada paciente individual.
Resumen
El acetato de megestrol es un progestágeno sintético potente con propiedades antiestrogénicas y glucocorticoides intrínsecas significativas.
Históricamente, se utilizó ampliamente en medicina veterinaria, particularmente en gatos, para diversas afecciones dermatológicas y conductuales. Sin embargo, su uso en felinos ha disminuido drásticamente en la práctica moderna debido al alto riesgo de efectos adversos graves, a veces irreversibles, que incluyen una supresión adrenocortical profunda y diabetes mellitus iatrogénica.
En perros, sigue estando aprobado por la FDA para el aplazamiento del estro y el alivio de la pseudogestación en hembras, y se utiliza fuera de indicación (off-label) para la hiperplasia prostática benigna (HPB) en machos. En medicina humana, se utiliza como estimulante del apetito y para el tratamiento paliativo de carcinomas avanzados de mama o de endometrio.
Mecanismo de acción
Megestrol acetate exerts its effects through multiple receptor pathways:
- Progesterone Receptors: Binds to progestin receptors → provides negative feedback to the hypothalamus and pituitary → inhibits the release of GnRH, LH, and FSH → suppresses estrus and ovulation.
- Glucocorticoid Receptors: Possesses significant intrinsic glucocorticoid activity → binds to glucocorticoid receptors → causes profound suppression of the hypothalamic-pituitary-adrenal (HPA) axis and induces insulin resistance.
- Anti-estrogenic Activity: Modifies target tissue response to estrogens.
Clinical Pearl: Unlike some other progestins, megestrol acetate does not possess significant anabolic or masculinizing effects on the developing fetus.
Seguridad y advertencias
Contraindicaciones
- Uterine disease (e.g., pyometra, endometritis)
- Diabetes mellitus
- Mammary neoplasias
- Prior to the first estrous cycle in dogs
- Anestrus therapy in dogs with abnormal cycles
- During diestrus or in the presence of uterine hemorrhage
- Treatment of pseudopregnancy in bitches (per manufacturer, though off-label protocols exist)
Efectos adversos
- Profound adrenocortical suppression (especially in cats)
- Transient or permanent diabetes mellitus
- Cystic endometrial hyperplasia (CEH) and pyometra
- Mammary hypertrophy and neoplasia
- Increased appetite and weight gain
- Polydipsia and polyuria (PU/PD)
- Lethargy and personality changes
- Hepatotoxicity (rare)
- Acromegaly (dogs)
- Lactation (rare)
Precauciones
Black Box Warning Equivalent: Megestrol acetate can induce profound, life-threatening adrenocortical suppression and iatrogenic Addisonian crisis, particularly in cats.
- Adrenal Suppression: Because of its glucocorticoid activity, patients may require exogenous stress-dose steroids during periods of trauma, surgery, or severe illness.
- Reproductive Risks: High risk of inducing cystic endometrial hyperplasia (CEH) and pyometra. A thorough reproductive history, physical exam, mammary palpation, and vaginal cytology are strongly recommended before initiating therapy for reproductive control.
- Infection Risk: May exacerbate latent viral infections (e.g., Feline Herpesvirus-1).
- Human Safety: Pregnant women should handle this medication with extreme caution (FDA Category X in early pregnancy).
Interacciones farmacológicas
Concurrent long-term use may exacerbate adrenocortical suppression and increase the risk of diabetes mellitus.
May decrease progestin activity due to microsomal enzyme induction, resulting in increased progestin metabolism.
Monitorización
- Body weight
- Blood glucose (draw baseline before therapy)
- Mammary gland development and appearance (nodules/hypertrophy)
- Adrenocortical function (ACTH stimulation test if indicated)
- Liver enzymes (especially with long-term treatment)
- Clinical efficacy
Farmacocinética
Vida media
Absorción
Well absorbed from the gastrointestinal tract.
Distribución
Widely distributed. Detectable amounts of progestins enter the milk of nursing mothers.
Metabolismo
Appears to be metabolized completely in the liver to conjugates and free steroids.
Eliminación
Excreted primarily via urine and feces.
Sobredosis
Acute toxicity from overdosage has not been reported. In humans, massive doses (up to 800 mg/day) caused no observable acute adverse reactions.
Chronic Toxicity in Dogs:
- Dosages of 0.1-0.25 mg/kg/day PO for 36 months yielded no gross abnormalities, but histologically, cystic endometrial hyperplasia (CEH) was noted (resolved when therapy was discontinued).
- Dosages of 0.5 mg/kg/day PO for 5 months caused reversible uterine hyperplasia.
- Dosages of 2 mg/kg/day demonstrated early cystic endometritis within 64 days.
Productos disponibles
Formulaciones
- Oral tablets
- Oral suspension
Veterinario
- Megestrol Acetate Oral Tablets: 5 mg, 20 mg (Ovaban)
Etiquetado para humanos
- Megestrol Acetate Tablets: 20 mg, 40 mg (Megace)
- Megestrol Acetate Suspension: 40 mg/mL, 125 mg/mL (Megace, Megace ES)
Estado regulador
Sin datos reguladores para: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Almacenamiento y estabilidad
Store tablets in well-closed containers at a temperature of less than 40°C. The veterinary manufacturer recommends storing the tablets from 2°-30°C (36°-86°F). Tablets may be crushed and administered with food.
Información para el cliente
El acetato de megestrol es un medicamento hormonal potente. Aunque puede ser eficaz, conlleva riesgos significativos, especialmente en gatos.
- Comprenda los riesgos: Este fármaco puede causar efectos secundarios graves, incluyendo diabetes, infecciones uterinas severas (piómetra) y supresión de las glándulas suprarrenales.
- Monitoree de cerca: Observe atentamente el consumo de agua y la micción de su mascota. Si comienza a beber o a orinar en exceso, contacte a su veterinario de inmediato, ya que podría ser un signo de diabetes.
- Cambios físicos: Revise regularmente las glándulas mamarias de su mascota (área del vientre) en busca de hinchazón, bultos o secreciones. Informe cualquier cambio a su veterinario.
- Comportamiento y energía: Tenga en cuenta cualquier letargo extremo, debilidad o cambios repentinos en el comportamiento.
- No suspenda el tratamiento abruptamente: Si su mascota ha estado tomando este medicamento a largo plazo, no lo suspenda repentinamente sin consultar a su veterinario, ya que su cuerpo puede necesitar tiempo para adaptarse.
- Seguridad humana: Las mujeres embarazadas deben evitar manipular este medicamento.
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.