ヒドロキシジン

Hydroxyzine

Hydroxyzine hydrochloride, Hydroxyzine pamoate

別名: Atarax · Vistaril · Masmoran · Ucerax · Hydroxyzine embonate · Hydroxyzine pamoate · Hydroxyzine HCl · Hydroxyzini HCl · Hydroxyzine hydrochloride

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

監査済み v13 用量エビデンス

構造化された用量計算エビデンス

体重

Antipruritic/antihistamine (extra-label)

2 mg/kgPO

q8-12h

必ず考慮する臨床コンテキスト (2)

■ This medicine may be given with or without food. If your animal drools, vomits, or acts sick after receiving this medicine on an empty stomach, give with food or a small treat to see if this helps.
Hydroxyzine oral products should be stored in tight, light-resistant containers at room temperature 20°C to 25°C (68°F-77°F). Hydroxyzine injection should be stored protected from light at room temperature 20°C to 25°C (68°F-77°F) with excursions permitted to 15°C to 30°C (59°F-86°F). Avoid freezing all liquid products.

formularyプロトコル 2023監査 dose-audit-plumb-v13

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

ヒドロキシジンは、獣医療で広く使用されている第一世代のピペラジン系抗ヒスタミン薬です。主に抗そう痒作用および抗ヒスタミン作用を目的として処方され、犬や猫のアトピー性皮膚炎、ノミアレルギー性皮膚炎などのアレルギー疾患の管理に頻用されます。

血液脳関門を通過するため、鎮静作用や精神安定作用も示し、不安を抱える動物や激しい痒みから自傷行為に及ぶ動物に非常に有効です。猫では、その鎮痙作用と軽度の抗不安作用により、頻回再発性の特発性下部尿路疾患（FLUTD）の管理に使用されることもあります。

作用機序

Hydroxyzine acts as a competitive antagonist at H1-receptors on effector cells.

Histamine Blockade: Competes with histamine for H1-receptor sites → prevents histamine-induced bronchoconstriction, vasodilation, and capillary permeability. Note: It does not inhibit the release of histamine from mast cells, but antagonizes its effects.
CNS Effects: Readily crosses the blood-brain barrier → binds to central H1 receptors → causes sedation and tranquilization.
Additional Properties: Exhibits anticholinergic, antispasmodic, local anesthetic, mild bronchodilative, and antiemetic activities.
Metabolism Pearl: In vivo, hydroxyzine is metabolized in the liver to its active metabolite, cetirizine, which contributes significantly to its prolonged antihistaminic effects.

安全性・警告

禁忌

Hypersensitivity to hydroxyzine or its metabolites (e.g., cetirizine)
Known hypersensitivity to hydroxyzine or cetirizine
Early pregnancy (teratogenic in some animal models)

有害事象

Sedation (most common, usually mild and transient in dogs)
Hyperexcitability (occasional paradoxical reaction)
Fine rapid tremors (dogs)
Whole body tremors (dogs)
Seizures (rare in dogs)
Polydipsia (cats)
Depression (cats)
Behavioral changes (cats)
Sedation / Lethargy
Dry mouth
Urinary retention
Gastrointestinal upset
Paradoxical excitation (rare)

注意事項

Use with caution in patients with prostatic hypertrophy, bladder neck obstruction, severe cardiac failure, angle-closure glaucoma, or pyeloduodenal obstruction due to its anticholinergic effects.

Pregnancy Warning: At doses substantially greater than those used therapeutically, hydroxyzine has been shown to be teratogenic in lab animals. Use during pregnancy (particularly during the first trimester) only when the benefits outweigh the risks (FDA Category C). It is unknown if hydroxyzine enters maternal milk, but its active metabolite cetirizine does.

医薬品相互作用

Anticholinergic agentsModerate

Additive anticholinergic effects may occur when used concomitantly.

CNS Depressant Drugs (e.g., barbiturates, tranquilizers)

Additive CNS depression may be seen.

Epinephrine

Hydroxyzine may inhibit or reverse the vasopressor effects of epinephrine; use norepinephrine or metaraminol instead.

CNS Depressants (e.g., opioids, barbiturates, gabapentin)Major

Additive CNS depression and sedation

監視

Efficacy (reduction in pruritus or clinical signs)
Adverse effects (degree of sedation, excitability, or behavioral changes)
Resolution of pruritus or allergic signs
Adverse anticholinergic effects (e.g., monitoring urination)

薬物動態

半減期

猫Unknown犬Approximately 4-6 hours

吸収

Rapidly and well absorbed after oral administration.

分布

Readily crosses the blood-brain barrier. It is unknown if hydroxyzine enters maternal milk, but its active metabolite cetirizine has been detected in milk.

代謝

Apparently metabolized in the liver (to its active metabolite, cetirizine).

消失

Effects generally persist for 6-8 hours in dogs and up to 12 hours in cats.

過剰投与

Overdoses would be expected to cause increased sedation and perhaps hypotension. At high doses, fine rapid tremors and rarely seizures have been reported.

Common clinical signs of toxicity in dogs include:

Hyperthermia
Lethargy
Tachycardia
Trembling / Tremors
Ataxia
Somnolence

Treatment: There are no specific antidotes available. Gut emptying protocols should be considered with large or unknown quantity overdoses. Supportive and symptomatic treatment is recommended if necessary.

製品

製剤

Oral Tablets
Oral Syrup
Injection
Oral Capsules
Oral Suspension
10 mg tablet
25 mg tablet
2 mg/ml syrup

ヒト用医薬品

Hydroxyzine HCl Oral Tablets: 10 mg, 25 mg, & 50 mg
Hydroxyzine HCl Oral Syrup: 10 mg/5 mL
Hydroxyzine HCl Injection: 25 mg/mL & 50 mg/mL
Hydroxyzine Pamoate Oral Capsules: 25 mg, 50 mg, & 100 mg
Hydroxyzine Pamoate Suspension: 25 mg/5 mL
Atarax 10 mg tablets
Atarax 25 mg tablets
Ucerax 2 mg/ml syrup

規制ステータス

European Union✓ 承認済み処方箋医薬品EMA

Classified as POM (Prescription Only Medicine).

United Kingdom✓ 承認済み処方箋医薬品VMD

Classified as POM (Prescription Only Medicine).

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

保管・安定性

Hydroxyzine oral products should be stored at room temperature in tight, light-resistant containers. Avoid freezing all liquid products.

飼主向け情報

眠気について：投薬開始時、ペットが眠そうにしたり、だるそうにしたりすることがあります。これは正常な反応ですが、過度な場合は獣医師にご相談ください。
使役犬への影響：この薬は、使役犬、猟犬、介助犬のパフォーマンスや注意力に影響を与える可能性があります。
継続的な投薬が重要：抗ヒスタミン薬は、症状がひどくなってから治療するよりも、アレルギーの悪化を「予防」するために継続的に投与する方が効果的です。
アレルギー検査：皮内アレルギー検査を予定している場合、検査の3〜7日前にこの薬の投与を中止する必要があります。正確な時期については獣医師にご相談ください。
2回分を一度に与えないでください：投薬を忘れた場合は、気づいた時に与えてください。ただし、絶対に2回分を一度に与えないでください。

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