Azithromycin
**Azithromycin** is a broad-spectrum, semi-synthetic macrolide antibiotic belonging to the azalide subclass. It is widely used in veterinary medicine due to its highly favorable pharmacokinetic profile, which allows for less frequent dosing compared to older macrolides like erythromycin. **Key Clinical Features:** * **Exceptional Tissue Penetration:** Azithromycin is actively taken up by phagocytes (macrophages and polymorphonuclear leukocytes) and fibroblasts, which then migrate to sites of infection. This results in tissue concentrations that can be up to 100 times higher than serum concentrations. * **Long Half-Life:** The drug exhibits a very long tissue half-life (up to 90 hours in dogs), allowing for pulse-dosing regimens (e.g., every 3 to 5 days) after an initial loading phase. * **Spectrum of Activity:** Effective against a variety of Gram-positive organisms (e.g., *Streptococcus*, *Staphylococcus*), some Gram-negative organisms (*Haemophilus*, *Bordetella*), and atypical pathogens including *Mycoplasma pneumoniae*, *Borrelia burgdorferi*, *Toxoplasma* spp., and *Bartonella* spp. * **Specific Uses:** Frequently utilized for canine *Bordetella* pneumonia, feline upper respiratory infections, feline Bartonellosis, *Babesia gibsoni* in dogs (in combination with atovaquone), and *Rhodococcus equi* infections in foals. > **Clinical Pearl:** Despite its broad utility, azithromycin has been shown to be ineffective for clearing *Chlamydophila felis* or *Mycoplasma haemofelis* in cats.
กลไกการออกฤทธิ์: Azithromycin exerts its antibacterial effects by binding to the **50S ribosomal subunit** of susceptible microorganisms. * **Mechanism:** By binding to the 50S subunit, it blocks **transpeptidation** and **translocation** processes → inhibits RNA-dependent protein synthesis. * **Action Type:** It is generally considered **bacteriostatic**, but can be bactericidal at high concentrations or against highly susceptible organisms. * **Targeted Delivery:** The drug is actively transported to the site of infection by host phagocytic cells. During active phagocytosis, azithromycin is released locally, providing high concentrations directly at the site of bacterial invasion.
ขนาดยาตามชนิดสัตว์
- Susceptible infections · 5-10 mg/kg PO once daily for 3-5 days · PO · q24h · 3-5 days
- Susceptible infections (pulse dosing) · 5 mg/kg PO once daily for 2 days, then every 3-5 days for a total of 5 doses · PO · q24h then q3-5d · 5 doses total
- 'Derm' infections · 5-10 mg/kg PO once daily for 5-7 days. For animals that are difficult to pill, a dose given every 5 days (after the initial 5-7 day course of therapy) may be effective if continued treatment is necessary. · PO · q24h then q5d · 5-7 days initially
- Canine pyoderma · 10 mg/kg PO once daily for 5-10 days · PO · q24h · 5-10 days
- Babesia gibsoni (Asian genotype) infections · Atovaquone 13.3 mg/kg PO q8h with a fatty meal and Azithromycin 10 mg/kg PO once daily. Give both drugs for 10 days. · PO · q24h · 10 days · Reserve immunosuppressive therapy for cases that are not rapidly responding (3-5 days) to anti-protozoal therapy.
- Idiopathic lymphoplasmacytic (chronic) rhinitis · Doxycycline 3-5 mg/kg PO q12h, or azithromycin 5 mg/kg PO q24h in combination with piroxicam 0.3 mg/kg PO q24h. · PO · q24h · Long term · Used for immunomodulatory effects.
- Susceptible infections · 5-10 mg/kg · PO · q24h · May increase dosing interval to q48h after 3-5 days of treatment · Doses are empirical and subject to change
- Chlamydiosis (experimentally infected cockatiels) · Azithromycin 40 mg/kg PO once every other day (q48h) for 21 days · PO · q48h · 21 days · Birds were dosed via metallic feeding tube into crop using the commercially available human oral suspension.
วิธีการให้ยา
ข้อห้ามใช้
- Hypersensitivity to azithromycin or any other macrolide antibiotics
อาการไม่พึงประสงค์
- Vomiting (especially at high doses)
- Diarrhea
- GI cramping
- Potential hepatotoxicity
- Local tissue reactions (IV site)
- Muscle damage (IM injection)
- Diarrhea in foals
อันตรกิริยาระหว่างยา
- Antacids (magnesium- and aluminum-containing) · May reduce the rate of absorption of azithromycin; separate dosages by 2 hours
- Cisapride · Other macrolides are contraindicated with cisapride due to potential for fatal arrhythmias; use with extreme caution or avoid
- Cyclosporine · Azithromycin may potentially increase cyclosporine blood levels; monitor carefully
- Digoxin · Other macrolides can increase digoxin levels; monitor carefully · major
- Pimozide · Contraindicated; acute deaths have occurred in humans
- Methylprednisolone · May increase serum levels of methylprednisolone · moderate
- Theophylline · May increase serum levels of theophylline · major
- Terfenadine · May increase serum levels of terfenadine · major
การติดตาม
- Clinical efficacy (resolution of infection signs)
- Adverse effects (especially GI distress or signs of hepatic impairment)
การได้รับยาเกินขนาด
Acute oral overdoses are unlikely to cause significant morbidity other than gastrointestinal distress, including **vomiting, diarrhea, and GI cramping**. Treatment should be supportive and symptomatic.
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