クロニジン
クロニジンは**中枢性α2アドレナリン受容体作動薬**であり、獣医学においては伝統的に犬の成長ホルモン（GH）欠乏症や褐色細胞腫の診断薬として使用されています。また、難治性の**炎症性腸疾患（IBD）**（特に猫）の補助治療や、重度の疼痛または外科麻酔のための硬膜外補助薬としても機能します。 > **臨床のポイント（薬理学的補足）：** > * モノグラフでは診断および胃腸への用途が強調されていますが、現代の獣医行動医学において、クロニジンは犬の**恐怖性不安、音響恐怖症、状況的パニック**を管理するための適応外使用が増加しています。 > * 交感神経の覚醒を抑えることで抗不安作用と鎮静作用を提供し、他の鎮静剤で見られるような重度の運動失調を伴わないことが多いです。 > * 心血管系への影響があるため、患者の慎重な選択と用量調整が必要です。
作用機序: Clonidine acts centrally at the **brain stem**, stimulating **alpha-2 adrenoreceptors**. * **Cardiovascular/Sympathetic:** Stimulation of presynaptic **alpha-2 receptors** (e.g., in the **locus coeruleus**) → decreases norepinephrine release → reduces sympathetic outflow from the CNS → decreased peripheral resistance, heart rate, and blood pressure. * **Endocrine:** Stimulates **GHRH (Growth Hormone Releasing Hormone)** → transient release of **Growth Hormone (GH)**. * **Analgesia:** Stimulates presynaptic and postjunctional **alpha-2 adrenoreceptors** in the dorsal horn of the spinal cord → blocks pain signal transmission to the brain. * **Gastrointestinal:** Alpha-2 stimulation alters enteric nervous system tone, increasing fluid absorption and decreasing motility, aiding in refractory IBD.
動物種別の用量
- Adjunctive antidiarrheal therapy for refractory cases of inflammatory bowel disease · 5-10 micrograms/kg · SC or PO · two to three times a day · As fourth line therapy after prostaglandin synthetase inhibitors, opioid agonists, and 5-HT3 serotonergic antagonists are being used.
- Epidural analgesia/analgesia · 2-3 micrograms/kg diluted to 8 mL with sterile normal saline · epidurally · Single dose · Onset/duration of analgesia = 19 minutes/192 minutes with 2 mcg/kg dose and = 9 minutes/311 minutes with 3 mcg/kg dose; peak effects from 60-180 minutes.
- Diagnosing hyposomatotropism · 10 micrograms/kg · IV · Single dose · Obtain plasma for GH levels prior to dosing and at 15, 30, 45, 60, and 120 minutes. Healthy dogs should demonstrate GH levels of 10 ng/mL after administration.
- Adjunctive antidiarrheal therapy for refractory cases of inflammatory bowel disease · 5-10 micrograms/kg · PO or SC · two to three times a day · Can activate alpha2-receptors in the CRT and cause vomiting.
- Control panic-like responses and fear-based behavioural problems · Dose not specified in monograph; use tactically (prn) or over longer term · PO · prn or daily · prn (lasts 3-4 hours) or long-term (takes 1-2 weeks for full response) · Effect develops in about 30 minutes. Withdrawal must be gradual.
- Diagnostic test for pituitary dwarfism (hyposomatotropism) · Dose not specified in monograph · IV · Single dose · N/A · Specialist texts should be consulted for the clonidine stimulation test protocol.
用量は獣医療従事者向けの臨床リファレンスです。必ず最新の添付文書と個々の患者で確認してください。
投与経路
禁忌
- Known hypersensitivity to clonidine
- Severe cardiovascular disease (use with extreme caution)
- Renal disease (use with extreme caution)
有害事象
- Transient hyperglycemia
- Dry mouth
- Constipation
- Sedation
- Aggressive behavior
- Hypotension
- Collapse
- Bradycardia
- Transient sedation
- Rebound hypertension (if withdrawn abruptly)
薬物相互作用
- Antihypertensive drugs · Possible additive hypotensive effects
- Beta-adrenergic blocking agents (e.g., propranolol) · May enhance bradycardia. If discontinuing, beta-blocker should be stopped first, then clonidine tapered to avoid rebound hypertension.
- CNS depressant drugs (opiates, barbiturates) · May exacerbate the actions of other CNS depressant drugs
- Digoxin · Possible additive bradycardia
- Prazosin · May decrease the antihypertensive effects of clonidine
- Tricyclic antidepressants (e.g., amitriptyline) · May block the antihypertensive effects of clonidine
- Barbiturates · Increased central nervous system depression and hypotension · major
- Opiates · Additive sedation, bradycardia, and respiratory depression · major
- Beta-blockers · Additive hypotensive and bradycardic effects; may exacerbate rebound hypertension upon withdrawal · major
- Hypotensive agents · Additive lowering of blood pressure · moderate
モニタリング
- Growth Hormone (GH) levels and adverse effects (when used for diagnostics)
- Blood pressure
- Heart rate
- Efficacy and adverse effect profile (when used for ongoing diarrhea treatment)
- Degree of sedation
- Behavioral response
- Plasma IGF-1 or GH levels (when used diagnostically)
過量投与
Clonidine has a **narrow margin of safety**. * **Clinical Signs:** Hypotension, bradycardia, vomiting, weakness, depression, lethargy, tachycardia, ataxia, and hypertension. Rarely, seizures or respiratory depression. * **Toxicity Values:** LD50 for oral clonidine in rats is 465 mg/kg; mice 206 mg/kg. * **Treatment:** For large overdoses, gut evacuation using standard protocols (use emetics cautiously as consciousness may deteriorate rapidly). Symptomatic and supportive care. Fluids and pressors (e.g., dopamine) for hypotension. IV atropine for bradycardia. **Atipamezole or yohimbine** may be used to reverse cardiovascular effects, but multiple doses may be required as signs can last up to 48 hours.
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。