酢酸メドロキシプロゲステロン
酢酸メドロキシプロゲステロン（MPA）は、プロゲステロンの強力な合成**プロゲスチン**誘導体です。 歴史的に、獣医学では行動修正（徘徊、オス間の攻撃行動、スプレー行動など）や皮膚疾患（猫の心因性脱毛症など）に使用されてきました。しかし、**重篤な副作用のリスクが高い**ため、現在では使用が大幅に減少しています。 **臨床のポイント:** 行動問題に対しては、より安全な代替治療（SSRI、TCA、または外科的避妊・去勢手術など）が強く推奨されます。MPAは、妊娠犬の黄体機能不全、良性前立腺肥大の短期管理、ジャーマン・シェパードの下垂体性小人症など、特定の生殖関連の適応症に現在でも時折使用されます。全身への影響が大きいため、内分泌および生殖器系の合併症という重大なリスクと潜在的な利益を慎重に比較検討する必要があります。
作用機序: MPA mimics endogenous progesterone by binding to intracellular **progesterone receptors**, translocating to the nucleus, and altering gene transcription. It transforms the proliferative endometrium into a secretory endometrium and inhibits spontaneous uterine contractions. * **Endocrine/Reproductive:** Exerts negative feedback on the hypothalamus and pituitary, decreasing **GnRH** → suppressing **FSH** and **LH** release, thereby inhibiting estrus and spermatogenesis. It also possesses anti-estrogenic properties and decreases plasma testosterone. * **Glucocorticoid Activity:** MPA has significant intrinsic affinity for **glucocorticoid receptors**, leading to profound suppression of the hypothalamic-pituitary-adrenal (HPA) axis (decreased ACTH and cortisol release). * **Metabolic Effects:** Induces peripheral insulin resistance, which can precipitate **diabetes mellitus**. * **Growth Hormone:** In dogs, progestins can stimulate the mammary glands to produce growth hormone, potentially leading to acromegaly.
動物種別の用量
- Behavioral disorders (reduce marking in neutered males) · 5-20 mg/kg SC or IM three to four times yearly · SC/IM · 3-4 times yearly · Use when all other drugs have been unsuccessful.
- Feline psychogenic alopecia and dermatitis · 75-150 mg IM or SC · IM/SC · Repeat as necessary, but never more often than every 2-3 months
- Progestagen-responsive dermatitis · 50-100 mg IM · IM · May repeat in 3-6 months if needed
- Recurrent abortion secondary to progesterone-deficiency · 1-2 mg/kg IM once weekly · IM · q7d · Stop treatment 7-10 days prior to parturition
- Long-term reproductive control · 2.5-5 mg PO once weekly; 25 mg injected every 6 months to postpone estrus · PO/IM/SC · q7d (PO) or q6mo (Injection)
- Long-term reproductive control · 2 mg/kg IM q5 months · IM · q5 months
- Management of spring transition, prevention of estrus behavior, induction of estrous cycle synchrony, pregnancy maintenance, modification of stallion behavior · 500 to 800 mg IM · IM · Interval varies · Most injections last 2 to 3 months · Will not prevent pregnancy loss and does not stop cyclicity.
- Antipruritic and to suppress ovulation · 0.025-1 mL (3 mg/100 grams body weight) IM once every 4-6 weeks · IM · q4-6w · May cause obesity, fatty liver, polydipsia/polyuria and lethargy if used repeatedly.
投与経路
禁忌
- Pre-pubescent cats or dogs
- Diabetes mellitus
- Pseudopregnant bitches
- Females in diestrus or with prolonged heat
- Uterine hemorrhage or discharge
- Pregnancy (unless specifically treating hypoluteoidism)
有害事象
- Increased thirst (polydipsia) and urination (polyuria)
- Increased appetite (polyphagia) and weight gain
- Depression, lethargy, and personality changes
- Adrenocortical depression (HPA axis suppression)
- Mammary changes (enlargement, milk production, neoplasia)
- Diabetes mellitus
- Pyometra / Cystic endometrial hyperplasia
- Temporary inhibition of spermatogenesis
- Permanent local alopecia, skin atrophy, and depigmentation (with SC injection)
- Acromegaly (in dogs)
薬物相互作用
- Aminoglutethimide · May decrease medroxyprogesterone effects
- Felbamate · May increase medroxyprogesterone metabolism
- Rifampin · May decrease progestin activity due to microsomal enzyme induction and increased progestin metabolism
モニタリング
- Weight
- Blood glucose (draw baseline before therapy and monitor periodically)
- Mammary gland development
- Adrenocortical function
- Clinical efficacy
過量投与
No specific reports on inadvertent acute overdosage were located. Overdose is expected to manifest as an exaggeration of adverse effects, including profound adrenal suppression, lethargy, metabolic derangements (hyperglycemia), and reproductive tract changes. Treatment should be supportive and symptomatic.
VetSheet の薬剤リファレンスは、獣医療従事者向けの臨床意思決定支援を目的としており、専門的判断やメーカーの最新添付文書に代わるものではありません。