アモキシシリン
アモキシシリンは、獣医療において様々な細菌感染症の治療に広く処方される**広域スペクトルアミノペニシリン**系抗生物質です。 主な薬理学的特徴は以下の通りです： * **抗菌スペクトル**: 多くのグラム陽性好気性菌、一部のグラム陰性好気性菌（大腸菌、クレブシエラ、ヘモフィルスなど）、および多くの偏性嫌気性菌（クロストリジウム属を含む）に対して有効です。 * **β-ラクタマーゼに対する感受性**: アンピシリンと同様に、β-ラクタマーゼ産生菌（黄色ブドウ球菌など）によって不活化されます。この耐性を克服するため、しばしばクラブラン酸と併用されます。 * **臨床的有用性**: 猫の膿瘍、感受性のある尿路感染症（UTI）、および軟部組織感染症に対する第一選択の経験的治療薬と見なされています。 * **薬物動態学的利点**: アンピシリンと比較して、単胃動物における経口バイオアベイラビリティが著しく高く、同等用量で1.5〜3倍の血清中濃度を達成します。
作用機序: 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.
動物種別の用量
- 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
投与経路
禁忌
- 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)
有害事象
- 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)
薬物相互作用
- 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
モニタリング
- Clinical efficacy (resolution of infection signs)
- Adverse effects (GI upset, signs of hypersensitivity)
過量投与
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.
VetSheet の薬剤リファレンスは、獣医療従事者向けの臨床意思決定支援を目的としており、専門的判断やメーカーの最新添付文書に代わるものではありません。