オキシトシン
Oxytocin
alpha-hypophamine
別名: Pitocin · Syntocinon · alpha-hypophamine · oxytocinum
VetSheet 獣医チームが監修更新日 2026年4月5日エビデンスに基づく獣医学リファレンス
0.5-3 Units SC or IM every 30-60 minutes, best based upon the results of tokodynamometry.SC/IM· q30-60m· Until parturition is complete
0.5–3 unit — 個体ごとの固定用量（体重換算なし）
用量は獣医専門家向けの臨床参考資料です。必ず最新の医薬品情報および個別症例に基づいて確認してください。
動物種別用量
🌎 NA — North America🌍 EU — Europe
犬
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| To augment uterine contractions during parturition | 0.5-3 Units SC or IM every 30-60 minutes, best based upon the results of tokodynamometry. | SC/IM | q30-60m | Until parturition is complete | 🌎 NA |
| For uterine inertia (if no fetuses in birth canal, cervix dilated, obstruction ruled out) | 5-20 Units (depending on size of animal) IM or as an IV drip (10 Units/liter) beginning as a slow drip and gradually increasing until effective contractions are observed. If no response to IM injection in 30 minutes, may repeat along with 10% dextrose IV slowly. If no response again in 30 minutes, repeat IM again. | IM/IV | As directed | — | 🌎 NA |
| For uterine inertia (mini-dose protocol) | 0.25 Units (total dose) SC or IM to a maximum dose of 4 Units per bitch. Generally not given more frequently than hourly. | SC/IM | q1h | — | 🌎 NA |
| To induce milk let-down (adequate milk production, tolerates nursing) | Oxytocin nasal spray: 5-10 minutes prior to nursing three times daily | Intranasal | TID | — | 🌎 NA |
| For secondary agalactia | 0.25-1 Unit (total dose) SC q2h. | SC | q2h | — | 🌎 NA |
| For adjunctive treatment of acute metritis | 0.5-5 Units (total dose) IM | IM | Once | — | 🌎 NA |
| To promote uterine involution after uterine prolapse manual reduction | 0.5-5 Units IM (Traas & O'Conner 2009) OR 5-10 Units (total dose) IM (Shaw 2007) | IM | Once | — | 🌎 NA |
- For uterine inertia (if no fetuses in birth canal, cervix dilated, obstruction ruled out): Some texts recommend giving calcium gluconate (2-10 mL slowly IV) prior. If no response, perform C-section.
- For uterine inertia (mini-dose protocol): Given 15 minutes after calcium gluconate 10% (1 mL/5.5 kg SC). Higher doses can cause tetanic contractions.
- For secondary agalactia: Remove neonates for 30 mins post-injection. Often used with metoclopramide 0.1-0.2 mg/kg SC q12h.
- For adjunctive treatment of acute metritis: May be used if birth occurred less than 24 hours prior.
- To promote uterine involution after uterine prolapse manual reduction: Given following successful manual reduction.
猫
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| To promote uterine involution after uterine prolapse manual reduction | 0.5-5 Units IM OR 5-10 Units (total dose) IM | IM | Once | — | 🌎 NA |
| To treat primary uterine inertia | 0.25 Units (total dose) SC or IM to a maximum dose of 4 Units per queen. Generally not given more frequently than hourly. | SC/IM | q1h | — | 🌎 NA |
| For adjunctive treatment of metritis | 0.5-5 Units IM | IM | Once | — | 🌎 NA |
| To induce milk let-down (secondary agalactia) | 0.25-1 Unit (total dose) SC q2h. | SC | q2h | — | 🌎 NA |
- To promote uterine involution after uterine prolapse manual reduction: Extrapolated from dog doses.
- To treat primary uterine inertia: Given 15 minutes after calcium gluconate.
- For adjunctive treatment of metritis: May be used if birth occurred less than 24 hours prior.
- To induce milk let-down (secondary agalactia): Remove neonates for 30 mins post-injection. Often used with metoclopramide.
小型哺乳類
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Uterotonic / Obstetrical use (Mice, Rats, Gerbils, Hamsters, Guinea pigs, Chinchillas) | 0.2-3 Units/kg IV, IM or SC | IV/IM/SC | Once | — | 🌎 NA |
鳥
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| As a uterotonic agent | 0.5 Units/kg IM; may repeat in 60 minutes | IM | May repeat in 60m | — | 🌎 NA |
| For egg expulsion | 0.01-0.1 mL once IM. | IM | Once | — | 🌎 NA |
- For egg expulsion: Should be administered with Vitamin A and calcium (injectable).
爬虫類
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| For egg binding | 1-10 Units/kg IM. | IM | As needed | — | 🌎 NA |
| To induce oviposition | 1-30 Units/kg (10 Units/kg appears effective in many chelonians). May have to repeat in several hours. | IM | May repeat in several hours | — | 🌎 NA |
- For egg binding: Given in combination with calcium glubionate. Use care with multiple injections. Not as effective in lizards.
- To induce oviposition: Risk of oviduct rupture if cloaca is obstructed.
馬
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| To augment or initiate uterine contractions during parturition in properly evaluated mares | 2.5-5 Units IV, every 15-20 minutes until foal is born | IV | q15-20m | Until foal is born | 🌎 NA |
| To prevent luteolysis (prolong corpus luteum lifespan) | 60 Units (3 ml) IM once daily from day 7 to day 14 post-ovulation. | IM | q24h | Days 7 to 14 post-ovulation | 🌎 NA |
| For evacuation of uterine fluid | 20 Units IV or IM one to three times a day | IV/IM | SID to TID | — | 🌎 NA |
| To aid in removal of retained fetal membranes | 30-100 Units in 1 liter of normal saline IV over 30-60 minutes OR 10-120 Units IM OR 10-40 Units by IV bolus | IV/IM | Once | — | 🌎 NA |
| To aid in removal of retained fetal membranes (alternative) | 20 Units IV or IM given every hour beginning 2-3 hours after foaling. Repeat as needed. | IV/IM | q1h | As needed | 🌎 NA |
| For mild to moderate cases of acute post-partum metritis | 20 Units IM 3-4 times a day for 2-3 days | IM | TID to QID | 2-3 days | 🌎 NA |
| To treat esophageal obstruction ('choke') | 0.11-0.22 Units/kg IV once | IV | Once | — | 🌎 NA |
- To prevent luteolysis (prolong corpus luteum lifespan): Ovulation must be documented closely.
- To aid in removal of retained fetal membranes: Large dose IV boluses are not recommended as they may cause uterine spasm and abdominal discomfort.
- To treat esophageal obstruction ('choke'): Given with N-butylscopolammonium bromide. Avoid or reduce dose in mares. Do not use in pregnant mares.
牛
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| For retained placenta | 40-60 Units oxytocin q2h as necessary. | IM/IV | q2h | As necessary | 🌎 NA |
| To reduce incidence of retained placenta | 20 Units IM immediately following calving and repeated 2-4 hours later | IM | Once, then repeat in 2-4h | — | 🌎 NA |
| For mild to moderate cases of acute post-partum metritis | 20 Units IM 3-4 times a day for 2-3 days | IM | TID to QID | 2-3 days | 🌎 NA |
| To augment uterine contractions during parturition | 30 Units IM; repeat no sooner than 30 minutes if necessary | IM | q30m | As necessary | 🌎 NA |
| For obstetrical use in cows | 100 Units IV, IM or SC | IV/IM/SC | Once | — | 🌎 NA |
| For milk let-down in cows | 10-20 Units IV | IV | Once | — | 🌎 NA |
- For retained placenta: Often used with IV calcium. Limited value after 48 hours postpartum.
豚
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| For adjunctive treatment of agalactia syndrome (MMA) in sows | 30-40 Units per sow at 3-4 hours | IM/IV | q3-4h | — | 🌎 NA |
| For adjunctive treatment of agalactia syndrome (MMA) in sows (alternative) | 20-50 Units IM or 5-10 Units IV | IM/IV | Once | — | 🌎 NA |
| For retained placenta in patients with uterine atony | 20-30 Units oxytocin q2-3h as necessary | IM/IV | q2-3h | As necessary | 🌎 NA |
| To augment uterine contractions during parturition | 10 Units IM; repeat no sooner than 30 minutes if necessary | IM | q30m | As necessary | 🌎 NA |
| For obstetrical use in sows | 30-50 Units IV, IM or SC | IV/IM/SC | Once | — | 🌎 NA |
| For mild to moderate cases of acute post-partum metritis | 5-10 Units IM 3-4 times a day for 2-3 days | IM | TID to QID | 2-3 days | 🌎 NA |
| For mild to moderate cases of acute post-partum metritis (alternative) | 5 Units IM; may need to be repeated as effect may be as short as 30 minutes | IM | As needed | — | 🌎 NA |
| For milk let-down in sows | 5-20 Units IV | IV | Once | — | 🌎 NA |
- For retained placenta in patients with uterine atony: Use with broad-spectrum antibiotics.
羊
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| For retained placenta in patients with uterine atony | 10-20 Units oxytocin. | IM/IV | Once | — | 🌎 NA |
| For mild to moderate cases of acute post-partum metritis | 5-10 Units IM 3-4 times a day for 2-3 days | IM | TID to QID | 2-3 days | 🌎 NA |
- For retained placenta in patients with uterine atony: Limited value after 48 hours postpartum. Note for CAMELIDS (NW): 5-10 Units IM at 10-minute intervals for retained placenta (Adams 2008).
ヤギ
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| For retained placenta in patients with uterine atony | 10-20 Units oxytocin. | IM/IV | Once | — | 🌎 NA |
| For mild to moderate cases of acute post-partum metritis | 5-10 Units IM 3-4 times a day for 2-3 days | IM | TID to QID | 2-3 days | 🌎 NA |
| To control post-extraction cervical and uterine bleeding after internal manipulations | 10-20 Units IV, may repeat SC in 2 hours | IV/SC | Once, may repeat in 2h | — | 🌎 NA |
- For retained placenta in patients with uterine atony: Limited value after 48 hours postpartum.
用量は獣医専門家向けの臨床参考資料です。必ず最新の医薬品情報および個別症例に基づいて確認してください。
概要
オキシトシンは、視床下部の室傍核および視索上核で合成され、下垂体後葉に貯蔵されるノナペプチドホルモンです。獣医学では主に子宮収縮薬として、分娩時の子宮収縮の誘発または増強、産後の胎盤停滞および子宮内膜炎の治療、子宮復古の促進、無乳症における乳汁分泌の促進に使用されます。
臨床上のポイント：
- ミニドーズの推奨： 現代の獣医産科学では、従来の高用量ではなく「ミニドーズ」（例：犬で総量0.25〜4単位）が強く推奨されています。高用量は強直性で無効な子宮収縮を引き起こし、胎盤圧迫による胎児の酸素供給低下や子宮破裂のリスクを高めます。
- カルシウム依存性： オキシトシンの有効性は細胞外カルシウムに大きく依存します。投与前に低カルシウム血症や低血糖を補正する必要があります。カルシウムは収縮の「強さ」を増し、オキシトシンは「頻度」を増します。
- 子宮頸管の状態： 子宮頸管が閉鎖している場合、または未矯正の閉塞性難産が存在する場合は、絶対に投与してはいけません。
作用機序
Oxytocin exerts its effects by binding to specific G-protein coupled oxytocin receptors (OXTR) on the cell membrane of uterine myofibrils and myoepithelial cells of the mammary gland.
- Uterine Contraction: Binding to OXTR activates the Gq/11 pathway → stimulates Phospholipase C (PLC) → increases inositol triphosphate (IP3) and diacylglycerol (DAG) → triggers the release of intracellular calcium from the sarcoplasmic reticulum. Calcium binds to calmodulin, activating Myosin Light Chain Kinase (MLCK), leading to smooth muscle contraction. The threshold for oxytocin-induced contraction is significantly lowered late in pregnancy due to upregulation of oxytocin receptors by high estrogen levels.
- Milk Let-down: Oxytocin stimulates the contraction of myoepithelial cells surrounding the mammary alveoli, forcing milk into the larger ducts and cisterns. It does not have galactopoietic (milk-producing) properties.
安全性・警告
禁忌
- Dystocia due to abnormal fetal presentation (unless corrected)
- Closed or unrelaxed cervix
- Known hypersensitivity to oxytocin
- Significant cephalopelvic disproportion
- Obstetrical emergencies where surgical intervention (C-section) is warranted
- Pregnancy (for nasally administered oxytocin)
有害事象
- Uterine cramping and discomfort
- Tetanic uterine contractions (at high doses)
- Uterine rupture
- Fetal compromise or death (due to placental compression)
- Water intoxication (with prolonged high-dose infusions)
- Hypersensitivity reactions (more common with non-synthetic products)
注意事項
Critical Warning: Always evaluate the patient for obstructive dystocia and ensure the cervix is dilated before administration.
- Metabolic Status: Treat hypoglycemia or hypocalcemia before using oxytocin, as uterine fatigue is often secondary to these metabolic deficits.
- Water Intoxication: While oxytocin has minimal antidiuretic properties, water intoxication can occur if administered at too rapid a rate or if excessively large volumes of electrolyte-free IV fluids are given concurrently. Signs include depression, coma, and seizures.
- Fetal Monitoring: Monitor fetal heart rates if possible, as excessive uterine contractions can cause fetal hypoxia.
医薬品相互作用
Thiopental
May delay thiopental anesthesia (reported in humans; clinical significance in animals is not firmly established).
Vasoconstrictors (Sympathomimetics)
Concurrent use post-partum may result in severe hypertension. Monitor closely.
監視
- Uterine contractions (frequency, duration, and strength via tokodynamometry if available)
- Status of the cervix (must be dilated)
- Fetal monitoring (heart rate/distress)
- Maternal calcium and glucose levels
薬物動態
吸収
Destroyed in the GI tract; must be administered parenterally. Intranasal absorption can be erratic. Uterine response is almost immediate after IV administration, and within 3-5 minutes following IM administration.
分布
Distributed throughout the extracellular fluid. Small quantities cross the placenta and enter the fetal circulation.
代謝
Metabolized rapidly in the liver and kidneys. A circulating enzyme, oxytocinase, can also destroy the hormone.
消失
Very small amounts are excreted unchanged in the urine. Duration of effect in dogs is ~13 minutes (IV) and ~20 minutes (IM/SC).
過剰投与
Effects of overdosage on the uterus depend on the stage of the uterus and the position of the fetus(es).
- Uterine Effects: Hypertonic or tetanic contractions can occur, leading to tumultuous labor, uterine rupture, fetal injury, or fetal death due to compromised placental blood flow.
- Water Intoxication: Can occur if large doses are infused for a long period, especially with large volumes of electrolyte-free IV fluids.
- Early signs: Listlessness, depression.
- Severe signs: Coma, seizures, death.
- Treatment: Stop oxytocin therapy, restrict water access. Severe cases may require osmotic diuretics (mannitol, urea, dextrose) with or without furosemide.
製品
製剤
- Injection (solution)
- Nasal spray
動物用医薬品
- Oxytocin for Injection: 20 USP Units/mL in 10 mL, 30 mL, and 100 mL vials
ヒト用医薬品
- Oxytocin Solution for Injection: 10 Units/mL in 1 mL amps, 3 mL & 10 mL vials and 10 mL multiple-dose vials (Pitocin®)
規制ステータス
規制データなし: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
保管・安定性
Store at temperatures less than 25°C (77°F); do not freeze. Some manufacturers recommend refrigeration (2-8°C), but some products are stable for up to 5 years if stored at less than 26°C.
飼主向け情報
オキシトシンは、ペットの分娩を助けたり、乳汁分泌を促すために使用される強力なホルモンです。
- 専門家による監視が必要： その効果を適切に監視できる獣医師の直接の指導または投与の下でのみ使用すべきです。
- 誤用のリスク： 胎児が引っかかっている場合や産道が完全に開いていない状態でオキシトシンを投与すると、子宮破裂や胎児の死亡など、深刻な合併症を引き起こす可能性があります。
- 点鼻スプレー： 乳汁分泌を促すために点鼻スプレーが処方された場合は、指示通りに（通常は授乳の5〜10分前に）投与してください。
VetSheet医薬品リファレンスは獣医専門家の臨床意思決定支援を目的としており、専門的判断または製造業者の最新医薬品情報の代替にはなりません。