トブラマイシン
トブラマイシンは、主に重篤なグラム陰性好気性細菌感染症に対して優れた有効性を示す、強力な非経口**アミノグリコシド系抗生物質**です。 **主な臨床的特徴：** * **抗菌スペクトル：** 好気性グラム陰性桿菌（緑膿菌、大腸菌、クレブシエラ、プロテウスなど）および一部の好気性グラム陽性菌（ブドウ球菌など）に対して高い有効性を示します。嫌気性菌および真菌には無効です。 * **臨床的有用性：** 固有の毒性があるため、全身投与は通常、他の毒性の低い抗菌薬が無効な重篤で生命を脅かす感染症、または既知のゲンタマイシン耐性株の治療に限定されます。 * **毒性プロファイル：** 全てのアミノグリコシド系と同様に、**腎毒性**および**耳毒性**の重大なリスクを伴います。一部の実験室データではゲンタマイシンより腎毒性がわずかに低い可能性が示唆されていますが、臨床的には依然として議論の余地があります。 > **臨床のポイント：** アミノグリコシド系は**濃度依存性の殺菌作用**と有意な**ポストアンチビオティックエフェクト（PAE）**を示します。このPK/PDプロファイルは、現代の高用量・投与間隔延長（1日1回）投与法を強く支持するものです。このアプローチにより、細菌死滅のための$C_{max}$/MIC比を最大化しつつ、腎尿細管細胞が薬物をクリアランスするための休薬期間を設け、腎毒性を最小限に抑えることができます。
作用機序: Tobramycin is a **bactericidal** antibiotic that disrupts bacterial protein synthesis. * **Cellular Entry:** The drug enters the bacterial cell via an **oxygen-dependent active transport mechanism**. > **Note:** Because this transport requires oxygen, aminoglycosides are completely ineffective against obligate anaerobic bacteria and have reduced efficacy in anaerobic environments (e.g., abscesses, necrotic tissue). * **Target Binding:** Once inside, tobramycin irreversibly binds to the **30S ribosomal subunit**. * **Mechanism:** Binding → misreading of mRNA → incorporation of incorrect amino acids into the growing peptide chain → production of non-functional or toxic proteins → bacterial cell death. * **Environmental Factors:** Antimicrobial activity is significantly enhanced in an **alkaline environment** and diminished in acidic, purulent conditions.
動物種別の用量
- General susceptible infections · 2 mg/kg · IV, IM, SC · q8h · Consider consolidating to once-daily dosing.
- Susceptible UTI · 1-2 mg/kg · SC · q8h
- Sepsis · 2-4 mg/kg · IV · q8h
- Soft tissue, systemic infections · 2 mg/kg IV, IM or SC q12h or 4 mg/kg IV, IM, SC q24h · IV, IM, SC · q12h or q24h · <= 5 days
- Persistent bacteremia · 2 mg/kg IV, IM, SC q8h or 6 mg/kg IV, IM or SC q24h · IV, IM, SC · q8h or q24h · <= 5 days
- Gram-negative infections · 4-6 mg/kg · IV/IM/SC · q24h · Assess according to clinical response · Cats may be more sensitive to toxicity. For severe infections (including sepsis), doses as high as 12 mg/kg/day have been advocated, but should be used with caution.
- Susceptible infections · 4 mg/kg · IV · q24h · Allows achievement of Cmax/MIC ratio higher than 10 for pathogen strains with a MIC of 1 microgram/mL.
- Susceptible infections · 5 mg/kg · IM · q12h
- Susceptible infections · 2.5-5 mg/kg/day · Parenteral · Daily
投与経路
禁忌
- Known hypersensitivity to aminoglycosides
- Rabbits and hares (causes fatal disruption of GI flora)
- Pre-existing severe renal disease (unless benefits outweigh risks)
- Dehydration
- Corneal ulceration (specifically for ophthalmic preparations)
有害事象
- Nephrotoxicity (acute tubular necrosis)
- Ototoxicity (vestibular and auditory damage, potentially irreversible)
- Neuromuscular blockade
- Facial edema
- Pain or inflammation at the injection site
- Peripheral neuropathy
- Hypersensitivity reactions
- Rarely: GI signs, hematologic, and hepatic effects
- Ototoxicity (vestibular and auditory damage)
- Neuromuscular blockade (rare)
薬物相互作用
- Beta-lactam antibiotics (penicillins, cephalosporins) · Synergistic antibacterial effects in vivo; however, can cause physical inactivation of aminoglycosides if mixed in the same syringe or IV line, or in vivo in patients with severe renal failure. · moderate
- Cephalosporins · Potential for additive nephrotoxicity (historically documented with older generation cephalosporins like cephalothin).
- Loop Diuretics (furosemide, torsemide) · Increased risk of nephrotoxicity and ototoxicity.
- Osmotic Diuretics (mannitol) · Increased risk of nephrotoxicity and ototoxicity.
- Other Nephrotoxic Drugs (cisplatin, amphotericin B, polymyxin B, vancomycin) · Significantly increased risk of acute kidney injury.
- Neuromuscular Blocking Agents & General Anesthetics · Concomitant use can potentiate and prolong neuromuscular blockade, potentially leading to respiratory paralysis.
- Amphotericin B · Increased risk of nephrotoxicity · major
- Furosemide · Increased risk of ototoxicity and nephrotoxicity · major
- Heparin · In vitro chemical inactivation if mixed · minor
- Pancuronium · Enhanced non-depolarizing neuromuscular blockade · moderate
モニタリング
- Clinical efficacy (resolution of fever, improved clinical signs, negative follow-up cultures)
- Renal toxicity: Baseline and serial urinalysis (monitoring for tubular casts, which are often the first sign of impending toxicity), urine specific gravity, serum creatinine, and BUN
- Gross monitoring for vestibular toxicity (head tilt, nystagmus, ataxia) or auditory toxicity (deafness)
- Therapeutic drug monitoring (peak and trough serum levels) is highly recommended to ensure efficacy and prevent toxicity
- Urinalysis (daily, looking for cellular casts as an early warning)
- Serum creatinine and BUN (baseline and periodically)
- Hydration status and urine output
- Auditory and vestibular function
過量投与
In the event of an inadvertent overdose, rapid intervention is required to prevent permanent renal and otic damage: * **Hemodialysis:** Highly effective in reducing serum levels of the drug, though rarely available in veterinary practice. * **Peritoneal Dialysis:** Can reduce serum levels but is significantly less efficacious than hemodialysis. * **Drug Complexation:** Intravenous administration of carbenicillin or ticarcillin (12-20 grams/day in humans) can complex with tobramycin in the blood, inactivating it. This is reportedly nearly as effective as hemodialysis.
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