VetSheet

シルデナフィル

Sildenafil

Sildenafil citrate

血管拡張薬 - ホスホジエステラーゼ5型 (PDE5) 阻害薬POIV犬猫

別名: Viagra · Revatio · Aphrodil · UK 92480-10 · Sildenafil citrate

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

1.9 mg/kg (range from 0.5-2.7 mg/kg)PO· q8-24h
— 🐕

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
Pulmonary hypertension1.9 mg/kg (range from 0.5-2.7 mg/kg)POq8-24h—🌎 NA
Pulmonary hypertension documented by Doppler, chronic pulmonary disease, right-sided heart failure (HW disease; congenital)0.5-1 mg/kg (higher dose of 2 -3 mg/kg three times a day may be tolerated and needed)POtwo times daily—🌎 NA
Moderate to severe PH secondary to either left heart disease or primary lung disease1 mg/kgPOq8h—🌎 NA
Pulmonary hypertension1-2 mg/kgPOthree times daily—🌎 NA
Pulmonary arterial hypertension0.5-2.7 mg/kg (suggested median dose from clinical studies is 3 mg/kg/day)POq8-24h—🌍 EU
  • Pulmonary hypertension: Median dose from a retrospective study. Dogs may have been also treated with oxygen, ACE inhibitors, furosemide, amlodipine, diltiazem, theophylline, phenobarbital and/or antibiotics.
  • Pulmonary arterial hypertension: Improves quality of life despite lack of significant echocardiographic reduction in pressures.

猫

適応用量経路頻度期間地域
Moderate to severe PH secondary to either left heart disease or primary lung disease1 mg/kgPOq8h—🌎 NA
Pulmonary arterial hypertension1.6 mg/kgPOq12h—🌍 EU
  • Pulmonary arterial hypertension: Reported dose tolerated and clinically efficacious.

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。

診察中ですか？VetSheet の AI が薬剤・用量・投与期間を構造化された診察記録に直接記入します。VetSheet の仕組みを見る

概要

シルデナフィルは強力な​ホスホジエステラーゼ5型（PDE5）阻害薬​です。人医療では主に勃起不全の治療薬として知られていますが、獣医薬理学においては​肺高血圧症（PH）​治療の要となる薬剤です。

  • ​臨床のポイント​: 慢性僧帽弁疾患、犬糸状虫症（フィラリア症）、または原発性肺疾患（肺線維症など）に続発する肺高血圧症の犬猫に対して特に有効です。
  • 肺動脈血管床を選択的に拡張することで、右室後負荷を著しく軽減し、失神、運動不耐性、右心不全などの臨床症状を改善します。
  • 肺血管に対する特異性が高いため、他の血管拡張薬と併用しない限り、通常は重篤な全身性低血圧を引き起こすことはありません。

作用機序

Sildenafil exerts its effects via the nitric oxide (NO) pathway in smooth muscle cells:

  • Endothelial cells release ​Nitric Oxide (NO)​ → activates the enzyme guanylate cyclase → converts GTP to ​cyclic guanosine monophosphate (cGMP)​.
  • cGMP acts as a secondary messenger causing smooth muscle relaxation and vasodilation.
  • PDE5 is the enzyme responsible for degrading cGMP, and it is found in high concentrations in the pulmonary vasculature and corpus cavernosum.
  • Mechanism: Sildenafil competitively inhibits PDE5 → prevents cGMP breakdown → intracellular cGMP accumulates → resulting in prolonged and enhanced NO-mediated pulmonary vasodilation.

安全性・警告

禁忌

  • Concurrent use with organic nitrates
  • Known hypersensitivity to sildenafil
  • Pulmonary veno-occlusive disease (PVOD)
  • Systemic hypotension
  • Significant hepatic impairment
  • Significant renal impairment
  • Bleeding disorders
  • Concurrent use of nitrates

有害事象

  • Cutaneous flushing of the inguinal region
  • Gastrointestinal effects (possible)
  • Headache, visual disturbances, dyspepsia, nasal congestion, myalgia, priapism, dizziness, and back pain (reported in humans)
  • Vomiting
  • Dizziness / weakness
  • Raised intraocular pressure
  • Systemic hypotension (especially if combined with other vasodilators)

注意事項

WARNING: Sildenafil should not be used concurrently with nitrates due to the risk of life-threatening hypotension.

  • Pulmonary vasodilators may significantly worsen the cardiovascular status of patients with pulmonary veno-occlusive disease (PVOD).
  • Use with extreme caution in patients with resting hypotension, fluid depletion, severe left ventricular outflow obstruction, or autonomic dysfunction.

医薬品相互作用

Alpha-adrenergic blockers (e.g., phentolamine, phenothiazines, phenoxybenzamine)

May increase hypotensive effects

Amlodipine

Potential to increase hypotensive effects

Antihypertensive, hypotensive drugs

Potentially could increase hypotensive effects

Azole antifungals (ketoconazole, itraconazole)

May reduce sildenafil metabolism and increase AUC

CimetidineModerate

May reduce sildenafil metabolism and increase AUC

Erythromycin, Clarithromycin

May reduce sildenafil metabolism and increase AUC

Heparin

May increase bleeding risks

Nitrates (e.g., NTG, Isosorbide)

Significant potentiation of vasodilatory effects; life-threatening hypotension possible

Nitroprusside sodium

Significant potentiation of vasodilatory effects; life-threatening hypotension possible

PhenobarbitalModerate

May decrease sildenafil concentrations

Rifampin

May decrease sildenafil concentrations

ErythromycinModerate

Increases plasma sildenafil concentration

ItraconazoleModerate

Increases plasma sildenafil concentration

Alpha-adrenergic blockersMajor

Increased risk of systemic hypotension; should not be started at the same time

NitratesMajor

Significantly enhances hypotensive effect; concomitant use must be avoided

監視

  • Clinical efficacy (improved syncope, cough, respiratory effort)
  • Pulmonary artery pressure
  • Systemic blood pressure
  • Adverse effects
  • Clinical signs of pulmonary hypertension (exercise tolerance, syncope, respiratory rate/effort)
  • Echocardiography (to monitor right heart function and pulmonary pressures)
  • Intraocular pressure (if pre-existing ocular disease)

薬物動態

半減期

犬approximately 6 hours (significant interpatient variability)

吸収

Oral bioavailability is approximately 50% in dogs (higher than humans).

分布

Volume of distribution is about 5.2 L/kg in dogs (versus 1.2 L/kg in humans).

代謝

Hepatic metabolism (implied by interactions with CYP inhibitors/inducers).

消失

Excreted primarily as metabolites.

過剰投与

Little information is available in veterinary species. In humans, massive overdose (2000 mg) resulted in tachycardia, nonspecific ST-T changes on ECG, headache, dizziness, and flushing.

It is expected that overdoses in animals would mirror the drug's adverse effect profile (e.g., profound hypotension, tachycardia, cutaneous flushing). ​Treat supportively.​

製品

製剤

  • Oral tablets
  • Injection solution
  • 20 mg tablet
  • 50 mg tablet
  • 6.25 mg tablet (special reformulation)
  • 10 mg tablet (special reformulation)
  • 12.5 mg tablet (special reformulation)
  • 10 mg/ml oral suspension
  • 0.08 mg/ml injectable (IV)

動物用医薬品

  • Special reformulations available: 6.25 mg, 10 mg and 12.5 mg tablets

ヒト用医薬品

  • Sildenafil Citrate Oral Tablets: 20 mg Revatio® (Pfizer); 25 mg, 50 mg & 100 mg Viagra® (Pfizer)
  • Sildenafil Injection Solution: 10 mg/12.5 mL (dextrose 50.5 mg/mL) in 12.5 mL single-use vials; Revatio® (Pfizer)
  • Revatio (20 mg tablets, 10 mg/ml oral suspension, 0.08 mg/ml IV)
  • Viagra (25 mg, 50 mg tablets)

規制ステータス

European Union✓ 承認済み処方箋医薬品EMA

POM (Prescription Only Medicine). Used off-label under the cascade.

United Kingdom✓ 承認済み処方箋医薬品VMD

POM-V / POM. Used off-label under the prescribing cascade.

規制データなし: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU

保管・安定性

Sildenafil tablets should be stored at room temperature (25°C; 77°F); excursions permitted to 15-30°C (59-86°F).

飼主向け情報

​重要​: シルデナフィルは、獣医療において肺の高血圧（肺高血圧症）を治療するために「適応外使用」として処方されることがよくあります。

  • ​期待される効果​: ペットの元気が出て、咳が減り、失神の発作が少なくなることに気づくかもしれません。
  • ​費用​: これは人間用の薬（Viagra®やRevatio®として知られています）であるため、高価になる場合があります。費用が心配な場合は、ジェネリック医薬品や調剤薬について獣医師に相談してください。
  • ​安全上の警告​: シルデナフィルを服用している間は、​絶対に​他の心臓薬、特に​硝酸薬​（ニトログリセリンなど）を与えないでください。致命的な血圧低下を引き起こす可能性があります。
  • ​副作用​: お腹（そけい部）の赤みやほてり、または胃腸の不調に注意してください。ペットがめまいを起こしたり、ぐったりしている場合、または倒れた場合は直ちに獣医師に連絡してください。

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。