ガバペンチン
ガバペンチンはγ-アミノ酪酸（GABA）の構造類似体であり、獣医療において主に**神経障害性疼痛の鎮痛**および**抗てんかん**作用のために広く使用されています。 * **鎮痛作用**：慢性疼痛、不適応疼痛、神経障害性疼痛（変形性関節症、椎間板疾患、がん性疼痛など）に非常に有効です。多くの場合、マルチモーダル鎮痛プロトコルの一部として使用されます。 * **てんかん管理**：難治性または複雑部分発作の補助的な抗てんかん薬（AED）として使用されますが、単独での有効性は限られています。 * **行動/抗不安**：動物病院への訪問やストレスの多い出来事の前に、恐怖、不安、ストレス（FAS）を軽減するために、犬や猫で適応外使用されることが増えています。
作用機序: Despite its name, gabapentin does *not* bind to GABA receptors, nor does it affect GABA synthesis or uptake. * Binds selectively to the **α2-δ (alpha-2-delta) subunit** of **voltage-gated calcium channels (CaV)** in the central nervous system. * **Inhibition of Calcium Influx** → Decreased presynaptic calcium currents. * **Reduced Neurotransmitter Release** → Suppresses the release of excitatory neurotransmitters including **glutamate**, **substance P**, and **norepinephrine** in the dorsal horn of the spinal cord. * This dampens neuronal excitability, effectively preventing **allodynia** (pain from non-noxious stimuli) and **hyperalgesia** (exaggerated pain response).
動物種別の用量
- Ancillary therapy of refractory seizures · 5-10 mg/kg · PO · q8-12h
- Ancillary therapy of refractory seizures · 5 mg/kg · PO · three times daily
- Ancillary therapy of refractory seizures · 10-30 mg/kg · PO · q8-12h
- Analgesic · 1.25-10 mg/kg · PO · q24h
- Adjunctive treatment of chronic or cancer pain · 3 mg/kg · PO · once a day
- Adjunctive analgesia associated with neuropathic pain · 2.5-5 mg/kg · PO · q12h · Author starts at 5 mg/kg and increases (up to 10 mg/kg) if no effect seen in two hours. Wean off slowly. Reduce in renal insufficiency.
- Analgesic · 5-10 mg/kg · PO · 2-3 times a day · Most VIN consultants recommend this dose.
- Analgesic · 50 mg (total dose) per cat · PO · 1-3 times a day
- Adjunctive seizure therapy / Chronic pain · 5-10 mg/kg · PO · q8-12h · starting dose; incremental dose increases are recommended
- Ancillary therapy of refractory seizures · 10-20 mg/kg · PO · q6-8h · Author notes gabapentin is the least effective of the newer antiepileptic drugs, particularly in dogs.
- Ancillary therapy of refractory seizures · 10-30 mg/kg · PO · q8-12h
投与経路
禁忌
- Hypersensitivity to gabapentin
- Use of xylitol-containing human oral solutions in dogs
- Oral solutions containing xylitol (highly toxic to dogs)
有害事象
- Sedation
- Ataxia
- Dizziness (humans)
- Somnolence
- Peripheral edema (humans)
- Withdrawal-precipitated seizures (if abruptly discontinued)
- Increased rate of pancreatic adenocarcinoma (noted in male rats)
- Mild sedation
- False-positive urinary protein tests (reported in humans)
- Hepatic toxicity (rare, reported in humans)
薬物相互作用
- Antacids · Oral antacids given concurrently may decrease oral bioavailability of gabapentin by 20%; separate doses by at least 2 hours.
- Hydrocodone · Co-administration may increase gabapentin AUC and efficacy/adverse effects. Gabapentin may reduce hydrocodone AUC, potentially reducing its effectiveness.
- Morphine · May increase gabapentin levels.
- Antacids (containing aluminium and magnesium) · Reduced absorption of gabapentin from the GI tract. Administer gabapentin at least 2 hours after antacids. · moderate
- Cimetidine · Reduced renal clearance of gabapentin (not considered clinically important). · minor
モニタリング
- Clinical efficacy (reduction in pain scores or seizure frequency)
- Adverse effects (sedation, ataxia)
- Renal function (in patients with pre-existing disease)
- Clinical response (pain scores, seizure frequency)
- Renal and hepatic function in compromised patients
過量投与
In humans, massive overdoses (up to 49 grams) have been reported without fatality. * **Clinical Signs**: Ataxia, lethargy, somnolence, vomiting, and diarrhea. * **Xylitol Toxicity Risk**: The human oral solution contains 300 mg/mL of xylitol. Doses as low as 0.33 mL/kg of this solution can cause severe hypoglycemia or hepatotoxicity in dogs. * **Treatment**: Primarily supportive. General decontamination (emesis, activated charcoal, cathartics) if caught early. The drug can be removed via hemodialysis. If xylitol toxicity is suspected secondary to the human liquid formulation, aggressive treatment for hypoglycemia and liver protection is required; contact an animal poison control center.
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。