阿莫西林
阿莫西林（Amoxicillin）是獸醫學中廣泛開立的**廣效氨基青黴素**抗生素，用於治療多種細菌感染。 主要藥理特徵包括： * **抗菌譜**：對許多革蘭氏陽性需氧菌、部分革蘭氏陰性需氧菌（如大腸桿菌、克雷伯氏菌、嗜血桿菌）及許多絕對厭氧菌（包含梭狀芽孢桿菌屬）有效。 * **對β-內醯胺酶的敏感性**：與氨苄西林（Ampicillin）相同，會被產生β-內醯胺酶的細菌（如金黃色葡萄球菌）去活化。臨床上常與克拉維酸（Clavulanate）結合使用以克服此抗藥性。 * **臨床應用**：被認為是貓膿瘍、敏感性泌尿道感染（UTIs）及軟組織感染的第一線經驗性治療首選。 * **藥代動力學優勢**：與氨苄西林相比，阿莫西林在單胃動物中的口服生物利用度顯著較佳，在同等劑量下可達到1.5至3倍的血清濃度。
作用機制: Amoxicillin is a **time-dependent, bactericidal** antibiotic that disrupts bacterial cell wall synthesis. * **Mechanism**: The beta-lactam ring mimics the D-alanyl-D-alanine terminal of the peptidoglycan precursor. * **Pathway**: Amoxicillin binds to specific **penicillin-binding proteins (PBPs)** (such as transpeptidases, carboxypeptidases, and endopeptidases) located on the inner surface of the bacterial cell membrane → inhibits the cross-linking of mucopeptide (peptidoglycan) chains → compromises the structural integrity of the cell wall → creates an osmotically unstable spheroplast → results in **cell lysis and death**. * **Efficacy**: It is most effective against actively dividing and growing bacteria.
各物種劑量
- Gram-positive infections · 10 mg/kg PO, IM, SC twice daily for at least 2 days after symptoms subside. · PO, IM, SC · q12h · At least 2 days after symptoms subside
- Gram-negative infections · 20 mg/kg PO three times daily or IM, SC twice daily for at least 2 days after symptoms subside · PO, IM, SC · q8h (PO) or q12h (IM, SC) · At least 2 days after symptoms subside
- Susceptible UTI's · 10-20 mg/kg PO q12h for 5-7 days. · PO · q12h · 5-7 days
- Susceptible systemic infections (bacteremia/sepsis) · 22-30 mg/kg IV , IM, SC q8h for 7 days. · IV, IM, SC · q8h · 7 days
- Susceptible orthopedic infections · 22-30 mg/kg IV , IM, SC, or PO q6-8h for 7-10 days. · IV, IM, SC, PO · q6-8h · 7-10 days
- Lyme disease · 22 mg/kg PO q12h for 21-28 days · PO · q12h · 21-28 days
- Susceptible urinary tract infections · 11 mg/kg PO q8h. · PO · q8h
- Preventative therapy for repeated (>2 per 6 months) urinary tract Gram-positive bacterial infections · 20 mg/kg PO once daily before bedtime after the dog has urinated. · PO · q24h · Use only after effective treatment completed using full therapeutic doses.
- Susceptible bacterial infections · 7 mg/kg · IM · q24h
- Susceptible bacterial infections (depot preparations) · 15 mg/kg · IM · q48h · For depot preparations only
給藥途徑
禁忌症
- Patients with a history of hypersensitivity to penicillins
- Oral administration in hindgut fermenters (rabbits, guinea pigs, chinchillas, hamsters) due to risk of fatal clostridial enterotoxemia
- Oral administration in patients with septicemia, shock, or grave illness (due to delayed/diminished GI absorption)
不良反應
- Gastrointestinal upset (anorexia, vomiting, diarrhea)
- Antibiotic-associated diarrhea and gut flora alteration
- Hypersensitivity reactions (rashes, fever, anaphylaxis)
- Eosinophilia, neutropenia, agranulocytosis, thrombocytopenia, leukopenia, anemias
- Lymphadenopathy
- Neurotoxicity (e.g., ataxia) at very high doses or prolonged use
- Elevated liver enzymes (rare)
- Tachypnea, dyspnea, edema, and tachycardia (reported in dogs)
藥物相互作用
- Bacteriostatic antimicrobials (e.g., chloramphenicol, macrolides, tetracyclines, sulfonamides) · Potential in vitro antagonism; concurrent use has historically been discouraged, though clinical significance is debated.
- Methotrexate · Amoxicillin may decrease the renal excretion of methotrexate, leading to increased levels and potential toxicity.
- Probenecid · Competitively blocks the tubular secretion of penicillins, increasing serum levels and prolonging serum half-life.
- Aminoglycosides · In vitro inactivation of aminoglycosides by beta-lactams; may falsely decrease aminoglycoside serum concentrations if samples are stored prior to analysis.
- Tetracycline · Potential antagonism of bactericidal activity (bacteriostatic vs bactericidal) · moderate
- Erythromycin · Potential antagonism of bactericidal activity · moderate
- Chloramphenicol · Potential antagonism of bactericidal activity · moderate
- Aminoglycosides (in vitro) · Inactivation of aminoglycoside if mixed in the same syringe · major
- Aminoglycosides (in vivo) · Synergistic antimicrobial effect when used concurrently
監測
- Clinical efficacy (resolution of infection signs)
- Adverse effects (GI upset, signs of hypersensitivity)
過量
Acute oral penicillin overdoses are unlikely to cause significant problems other than **gastrointestinal distress** (vomiting, diarrhea, anorexia). In humans, very high dosages of parenteral penicillins, especially in patients with compromised renal function, have induced **CNS effects** (e.g., seizures, ataxia). Treatment is generally supportive and symptomatic.
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