フェノバルビタール

動物種別の用量

投与経路

禁忌

• Known hypersensitivity to barbiturates
• Severe liver disease
• Nephritis (large doses)
• Severe respiratory depression
• Hepatic dysfunction
• Severe renal impairment
• Hypersensitivity to barbiturates

有害事象

• Dogs: Transient anxiety, agitation, or lethargy upon initiation
• Dogs: Polydipsia (PD), polyuria (PU), and polyphagia (PP)
• Dogs: Sedation and ataxia (especially at higher serum levels)
• Dogs: Elevated liver enzymes (ALT, ALP) - common and not always indicative of failure
• Dogs: Hepatotoxicity (uncommon, usually at levels >30-40 mcg/mL)
• Dogs: Rare blood dyscrasias (anemia, thrombocytopenia, neutropenia)
• Dogs: Rare superficial necrolytic dermatitis (SND)
• Cats: Ataxia, persistent sedation, lethargy
• Cats: Polyphagia, weight gain, PU/PD
• Cats: Rare immune-mediated reactions and bone marrow hypoplasia
• Cats: Coagulopathies (at very high doses)
• Sedation
• Ataxia
• Polyuria (PU)
• Polydipsia (PD)

薬物相互作用

• Acetaminophen · Increased risk for hepatotoxicity, particularly with large or chronic doses of barbiturates.
• Carprofen · Increased risk for hepatotoxicity secondary to carprofen metabolites.
• MAO Inhibitors (e.g., Selegiline) · May prolong phenobarbital effects.
• Phenytoin · Barbiturates may affect phenytoin metabolism, and phenytoin may alter barbiturate levels.
• Rifampin · May induce enzymes that increase the metabolism of barbiturates.
• Levetiracetam · Phenobarbital reduces levetiracetam elimination half-life by about 50% in dogs.
• Warfarin · Phenobarbital may decrease anticoagulant effects by lowering serum concentrations.
• Corticosteroids · Phenobarbital increases the metabolism and clearance of corticosteroids, potentially reducing their efficacy. · moderate
• Doxycycline · Phenobarbital decreases doxycycline serum concentrations; effect may persist for weeks after discontinuation.
• Theophylline · Phenobarbital increases theophylline metabolism, lowering its serum concentrations.
• Chloramphenicol · May increase the effects of phenobarbital while phenobarbital may decrease chloramphenicol levels. · major
• Levothyroxine · Increased hepatic metabolism and clearance of T4 · moderate

モニタリング

• Anticonvulsant efficacy (seizure frequency and severity)
• Adverse effects (CNS depression, ataxia, PU/PD, weight gain)
• Serum phenobarbital levels (Dogs: 20-35 mcg/mL; Cats: 23-30 mcg/mL). Wait 5-6 half-lives (12-14 days in dogs, 9-10 days in cats) before measuring steady-state levels.
• Routine CBC, liver enzymes (especially ALT and AST), and bilirubin at least every 6 months during chronic therapy.
• Serum phenobarbital concentrations (trough levels)
• Liver enzymes (ALT, ALP, GGT)
• Serum bile acids
• Complete Blood Count (CBC)
• Renal function

過量投与

**Clinical Signs of Toxicity**: * **Dogs**: Ataxia, lethargy, sedation, recumbency, depression, hypothermia, and coma. * **Cats**: Ataxia, sedation, and recumbency. **Treatment**: * **Decontamination**: Removal of ingested product from the gut if recent. **Activated charcoal** is highly effective and acts as a 'sink' to draw the drug from the vasculature back into the gut, enhancing clearance even if the drug was given parenterally. * **Supportive Care**: Provide intensive respiratory and cardiovascular support. * **Enhanced Elimination**: Forced alkaline diuresis can substantially augment elimination in patients with normal renal function. Peritoneal dialysis or hemodialysis may be helpful in severe intoxications or anuric patients.