ジアゼパム
ジアゼパムは、獣医学において抗不安、筋弛緩、催眠、食欲増進、および抗けいれん作用のために広く利用される、古典的で長時間作用型の**ベンゾジアゼピン系**誘導体です。 **臨床上のポイント:** * **てんかん管理:** ジアゼパムは、てんかん重積状態や群発てんかんの緊急治療における第一選択薬です。しかし、作用時間が短く、急速に耐性が形成されるため、犬の長期的な維持抗けいれん薬としては一般的に無効です。 * **猫に関する注意事項:** 猫では耐性の問題は少ないものの、特異体質による致命的な**劇症肝壊死**のリスクがあるため、経口投与は非常に議論の余地があります。 * **製剤の特徴:** 注射剤には**プロピレングリコール**が含まれており、静脈内へ急速に投与すると低血圧、徐脈、心毒性を引き起こす可能性があります。また、PVCプラスチックに吸着しやすいため、プラスチック製シリンジでの保管や標準的な輸液バッグによる長時間の投与には適していません。
作用機序: Diazepam exerts its effects by binding to specific allosteric sites on **GABA-A receptors** in the central nervous system (primarily in the limbic system, thalamus, and hypothalamus). * Binding to the benzodiazepine site → enhances the affinity of the inhibitory neurotransmitter **gamma-aminobutyric acid (GABA)** for its receptor. * This facilitation → increases the frequency of chloride channel opening → influx of chloride ions → **neuronal hyperpolarization**. * The resulting hyperpolarization leads to profound CNS depression, producing anxiolytic, sedative, muscle relaxant, and anticonvulsant effects.
動物種別の用量
- Urine marking and anxiety · 0.2-0.4 mg/kg (start at 0.2 mg/kg PO q12h) · PO · q12-24h
- Spraying · 1-2.5 mg per cat · PO · q8-12h · Sedation and ataxia should abate within several days.
- Fast-acting anxiolytic · 0.2-0.5 mg/kg · PO · prn
- Treatment of seizure disorders · 0.25-0.5 mg/kg · PO · q8-12h · Do not use if cat has been exposed to chlorpyrifos.
- Halt an ongoing seizure · 0.5-1 mg/kg · IV · prn · If cat has a history of receiving insulin, glucose may be more beneficial.
- Maintenance therapy for seizures · 0.2-1 mg/kg · PO · q12h · Use with caution; associated with fatal hepatic necrosis. Phenobarbital is preferred.
- Functional urethral obstruction/urethral sphincter hypertonus · 1-2.5 mg (total dose) · PO · q8h
- Functional urethral obstruction/urethral sphincter hypertonus · 2.5-5 mg (total dose) PO q8h or as needed, or 0.5 mg/kg IV · PO/IV · q8h or prn
- Short-term emergency control of severe epileptic seizures · Dose not specified in monograph · IV/Rectal · PRN · Short-term · Half-life is longer in cats; may be effective as maintenance, but oral use carries high risk of hepatic necrosis.
- Appetite stimulant · Dose not specified in monograph · PO/IV · PRN · Short-term · Use with extreme caution due to risk of liver injury.
投与経路
禁忌
- Known hypersensitivity to benzodiazepines
- Cats exposed to chlorpyrifos (potentiates organophosphate toxicity)
- Significant liver disease (especially in cats)
- Intra-carotid artery injections (must be strictly avoided)
- CNS depression
- Respiratory depression
- Severe muscle weakness
- Hepatic impairment (may worsen hepatic encephalopathy)
- Long-term treatment of behavioural disorders (due to risks of disinhibition and interference with memory/learning)
有害事象
- Sedation and ataxia (most common)
- Dogs: Paradoxical CNS excitement/agitation (especially at doses >0.8 mg/kg)
- Dogs: Increased appetite
- Cats: Idiosyncratic hepatic failure (with oral use)
- Cats: Behavior changes (irritability, depression, aberrant demeanor)
- Horses: Muscle fasciculations, weakness, ataxia, recumbency (at doses >0.2 mg/kg)
- Hypotension and phlebitis (with rapid IV injection)
- Sedation
- Muscle weakness
- Ataxia
- Paradoxical excitation and aggression (especially with rapid IV injection or oral overdose in dogs)
- Pain and erratic absorption (IM injection)
- Fulminant hepatic necrosis (cats, repeated oral dosing)
- Thrombophlebitis (associated with propylene glycol injectable formulations)
薬物相互作用
- Amitriptyline · May increase diazepam levels
- Antacids · May decrease oral diazepam absorption
- Azole Antifungals (itraconazole, ketoconazole) · May increase diazepam levels by inhibiting metabolism
- Cimetidine · May decrease metabolism of benzodiazepines · moderate
- CNS Depressants (barbiturates, narcotics, anesthetics) · Additive CNS depression effects may occur
- Dexamethasone · May decrease diazepam levels
- Digoxin · Diazepam may increase digoxin levels · moderate
- Erythromycin · May decrease the metabolism of benzodiazepines
- Mineral Oil · May decrease oral diazepam absorption
- Omeprazole · May inhibit the metabolism of diazepam and increase levels · moderate
- Phenobarbital · May decrease diazepam concentrations · moderate
- Phenytoin · May decrease diazepam concentrations
- Quinidine · May increase diazepam levels
- Rifampin · May induce hepatic microsomal enzymes and decrease the pharmacologic effects of benzodiazepines
モニタリング
- Horses should be observed carefully after receiving this drug.
- Cats receiving oral diazepam must have baseline liver function tests. Repeat and discontinue drug if emesis, lethargy, inappetence, or ataxia develop.
- When used for seizure control in cats, obtain serum levels 5 days after beginning therapy (therapeutic goal: 200-700 ng/mL or 2500-700 nmol/L).
- Hepatic function (especially in cats)
- Respiratory rate and effort
- Level of CNS depression / sedation
- Seizure activity
過量投与
When administered alone, diazepam overdoses are generally limited to significant **CNS depression** (confusion, coma, decreased reflexes, etc.). Hypotension, respiratory depression, and cardiac arrest have been reported in human patients, but are quite rare. **Treatment:** * Standard protocols for removing and/or binding the drug in the gut if taken orally (e.g., emesis, activated charcoal). * Supportive systemic measures (fluids, respiratory support if needed). * The use of analeptic agents (CNS stimulants like caffeine) is generally **not recommended**. * **Flumazenil** (a specific benzodiazepine antagonist) may be considered for adjunctive treatment of severe overdoses.
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