苯唑西林
苯唑西林（Oxacillin）是一種窄效的**抗β-內醯胺酶（抗葡萄球菌）青黴素**。 * **臨床用途**：主要用於治療由產青黴素酶的葡萄球菌（如MSSA、MSSP）引起的骨骼、皮膚及軟組織感染。 * **抗菌譜**：對革蘭氏陽性球菌高度有效。對立克次體、分枝桿菌、黴菌、黴漿菌、病毒及多數革蘭氏陰性菌無效。 * **抗藥性背景**：雖然它能抵抗葡萄球菌的β-內醯胺酶，但對**耐甲氧西林金黃色葡萄球菌 (MRSA)** 或 **耐甲氧西林偽中間葡萄球菌 (MRSP)** 無效，因為這些細菌具有不同的抗藥機制（透過*mecA*基因改變標靶位點）。 * **獸醫應用限制**：由於其半衰期極短（需每6-8小時給藥一次）、口服生物利用度差，且缺乏便利的獸醫專用口服劑型，目前在獸醫學中較少使用。臨床上通常更傾向使用頭孢菌素或阿莫西林-克拉維酸鉀以提高便利性。
作用機制: Oxacillin is a **bactericidal beta-lactam antibiotic**. * **Mechanism**: It covalently binds to **Penicillin-Binding Proteins (PBPs)** (specifically transpeptidases) located on the inner membrane of the bacterial cell wall. * **Pathway**: PBP binding → inhibition of the terminal transpeptidation step of peptidoglycan synthesis → weakened cell wall → osmotic instability → **cell lysis and death**. * **Enzyme Resistance**: The drug features a bulky isoxazolyl side chain that provides steric hindrance, preventing staphylococcal **beta-lactamase (penicillinase)** from hydrolyzing and destroying the beta-lactam ring.
各物種劑量
- Susceptible infections · 22-40 mg/kg PO, SC, IM, or IV q8h · PO, SC, IM, IV · q8h
- Susceptible infections · 20-30 mg/kg IV q6-8h · IV · q6-8h · Dose extrapolated from adult horse data; use lower dose or longer interval in premature foals or those less than 7 days old.
- Susceptible infections · 25-50 mg/kg IM, IV twice daily · IM, IV · q12h
- Susceptible infections · 22-40 mg/kg PO, SC, IM, or IV q8h · PO, SC, IM, IV · q8h
劑量為持牌獸醫專業人員的臨床參考。請務必對照最新藥品說明書及個別病患確認。
給藥途徑
禁忌症
- Known hypersensitivity to penicillins
- Oral administration in patients with septicemia, shock, or other grave illnesses (due to delayed/diminished GI absorption)
不良反應
- Anorexia
- Vomiting
- Diarrhea
- Antibiotic-associated diarrhea and superinfections
- Hypersensitivity reactions (rash, fever, eosinophilia, anaphylaxis)
- Neurotoxicity (ataxia, CNS effects at very high doses)
- Elevated liver enzymes
- Tachypnea
- Dyspnea
- Edema
- Tachycardia
藥物相互作用
- Aminoglycosides · In vitro evidence of synergism against S. aureus strains; however, mixing in the same syringe/fluid line can cause physical inactivation.
- Cyclosporine · Oxacillin may reduce cyclosporine serum levels.
- Probenecid · Competitively blocks the tubular secretion of oxacillin, thereby increasing serum levels and prolonging serum half-life.
- Tetracyclines · Theoretical antagonism (bacteriostatic drugs may interfere with bactericidal action of penicillins); concurrent use is usually not recommended.
- Warfarin · Oxacillin may cause decreased warfarin efficacy.
監測
- Clinical efficacy (resolution of infection)
- Signs of adverse effects (GI upset, allergic reactions)
過量
Acute oral overdoses are unlikely to cause significant problems other than **gastrointestinal distress** (vomiting, diarrhea). In humans, very high dosages of parenteral penicillins, especially in patients with compromised renal function, have induced **CNS effects and neurotoxicity**.
VetSheet 藥物參考供持牌獸醫專業人員作臨床決策輔助之用,不能取代專業判斷或廠方最新藥品說明書。