オルビフロキサシン
オルビフロキサシンは、主に獣医学で使用される合成広域**フルオロキノロン系抗生物質**です。**濃度依存性の殺菌作用**を示し、有意な**ポストアンチバイオティックエフェクト（PAE）**を持ちます。これは、薬物濃度が最小発育阻止濃度（MIC）を下回った後でも細菌の増殖が抑制され続けることを意味します。 好気性グラム陰性桿菌（大腸菌、クレブシエラ、プロテウス、エンテロバクター、パスツレラなど）および一部のグラム陽性球菌（スタフィロコッカス・インターメディウス、黄色ブドウ球菌など）に対して高い有効性を示します。 > **臨床のポイント：** 他のフルオロキノロン系と同様に、オルビフロキサシンは偏性嫌気性菌およびほとんどの腸球菌に対する有効性が低いです。抗菌薬の適正使用を促進するため、培養および感受性試験で必要性が示された感染症に限定して使用すべきです。
作用機序: Fluoroquinolones exert their bactericidal effect by targeting two essential bacterial enzymes: * **DNA Gyrase (Topoisomerase II):** The primary target in gram-negative bacteria. It prevents the relaxation of positively supercoiled DNA, which is required for normal transcription and replication. * **Topoisomerase IV:** The primary target in gram-positive bacteria. It interferes with the separation of interlinked replicated DNA molecules. **Mechanism Pathway:** Orbifloxacin binds to the enzyme-DNA complex → inhibits DNA replication and transcription → induces double-stranded DNA breaks → rapid bacterial cell death.
動物種別の用量
- Susceptible infections · 2.5 mg/kg-7.5 mg/kg · PO · once daily · Tablets. Higher end of the dosing range may be necessary for complicated infections.
- Skin infections (wounds and abscesses) · 7.5 mg/kg · PO · once daily · Suspension. For susceptible strains of S. aureus, E. coli, and P. multocida.
- Skin and other soft tissue infections · 7.5 mg/kg · PO · q24h · Caution with higher doses due to risk of retinal blindness.
- Susceptible infections · 5 mg/kg · PO · once daily
- Susceptible infections · 7.5 mg/kg · PO · once daily
- Susceptible infections · 2.5 mg/kg-7.5 mg/kg · PO · once daily · Tablets. Higher end of the dosing range may be necessary in hospitalized patients, those with underlying disease, structural alterations, or infections caused by 'problem' pathogens.
- Urinary tract infections (cystitis) and skin/soft tissue infections (wounds and abscesses) · 2.5-7.5 mg/kg · PO · once daily · Suspension.
- Bacterial cystitis · 2.5 mg/kg · PO · q24h
- Skin and other soft tissue infections · 7.5 mg/kg · PO · q24h
投与経路
禁忌
- Immature dogs during the rapid growth phase (2-8 months in small/medium breeds; up to 18 months in large/giant breeds)
- Known hypersensitivity to orbifloxacin or other quinolones
- Giant-breed dogs <18 months old
- Large breeds <12 months old
- Small and medium-sized breeds <8 months old
- Pregnant or lactating bitches
- Animals intended for breeding
- Animals <4 months of age (otic preparation)
- Animals with a ruptured tympanum (otic preparation)
有害事象
- Anorexia
- Vomiting
- Diarrhea
- Arthropathies (cartilage damage) in immature, growing animals
- Potential retinal toxicity/blindness in cats (rare, but reported with higher doses of fluoroquinolones)
- CNS stimulation (rare)
- Cartilage abnormalities in growing animals
- CNS adverse effects (potentiated by NSAIDs)
- Retinal blindness in cats (dose-dependent)
薬物相互作用
- Antacids / Dairy Products · Cations (Mg++, Al+++, Ca++) bind to orbifloxacin and prevent its absorption; separate doses by at least 2 hours.
- Other Antibiotics (Aminoglycosides, 3rd-gen cephalosporins, extended-spectrum penicillins) · Unpredictable synergism may occur against some bacteria (particularly Pseudomonas aeruginosa).
- Cyclosporine · May exacerbate nephrotoxicity and reduce the metabolism of systemic cyclosporine.
- Flunixin · May increase the AUC and elimination half-life of fluoroquinolones.
- Glyburide · Severe hypoglycemia is possible.
- Iron, Zinc (oral) · Decreased orbifloxacin absorption; separate doses by at least 2 hours.
- Methotrexate · Increased methotrexate levels possible, resulting in toxicity.
- Nitrofurantoin · May antagonize the antimicrobial activity of fluoroquinolones; concomitant use is not recommended.
- Phenytoin · May alter phenytoin levels.
- Probenecid · Blocks tubular secretion, potentially increasing blood levels and half-life of orbifloxacin.
- Sucralfate · May inhibit absorption of orbifloxacin; separate doses by at least 2 hours. · major
- Theophylline · May increase theophylline blood levels. · major
モニタリング
- Clinical efficacy (resolution of infection)
- Gastrointestinal signs (appetite, vomiting, diarrhea)
- Vision changes or pupillary dilation in cats
- Neurological signs (seizures) in predisposed patients
過量投与
In dogs, receiving up to 5X the maximum dose (37.5 mg/kg) for 30 days did not result in any significant adverse effects. In cats, receiving higher dosages exhibited soft feces and decreased body weight gains.
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