Erythromycin
Erythromycin is a **macrolide antibiotic** frequently utilized in veterinary ophthalmology. * **Spectrum of Activity:** Primarily effective against gram-positive organisms, with the notable exception of enterococci. * **Target Organisms:** In ophthalmic applications, it is specifically targeted towards infections caused by *Mycoplasma* spp., *Chlamydia* spp., and *Borrelia burgdorferi*. * **Clinical Utility:** Because resistance to erythromycin remains relatively limited among these specific atypical organisms, it serves as a highly valuable therapeutic option for ocular surface infections, particularly feline chlamydial and mycoplasmal conjunctivitis.
Mechanism: Erythromycin is a bacteriostatic macrolide antibiotic. * **Mechanism:** It reversibly binds to the **50S ribosomal subunit** of susceptible microorganisms. * **Pathway:** Binding to the 50S subunit → blockade of transpeptidation and/or translocation reactions → inhibition of RNA-dependent bacterial protein synthesis → suppression of bacterial growth.
Dosing by species
- Ophthalmic infections (Mycoplasma, Chlamydia, Borrelia) · ½ inch strip · topical ophthalmic · three to four times daily
- Ophthalmic infections (Mycoplasma, Chlamydia, Borrelia) · ½ inch strip · topical ophthalmic · three to four times daily
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Hepatic dysfunction (especially the estolate salt)
Adverse effects
- Gastrointestinal upset (most common)
- Cholestatic hepatitis (associated with estolate salt in humans)
Drug interactions
- Digoxin · May enhance the absorption of digoxin from the GI tract · moderate
- Ciclosporin · Increases serum levels of ciclosporin · major
- Cisapride · Increases serum levels of cisapride, leading to potentially fatal arrhythmias · major
- Methylprednisolone · Increases serum levels of methylprednisolone · moderate
- Theophylline · Increases serum levels of theophylline · major
- Terfenadine · Increases serum levels of terfenadine, leading to potentially fatal arrhythmias · major
- Macrolides · Antagonism may occur if used in combination · major
- Lincosamides · Antagonism may occur if used in combination · major
- Chloramphenicol · Antagonism may occur if used in combination (competes for 50S binding site) · major
Monitoring
- Gastrointestinal signs
- Hepatic function (especially if using estolate salt)
- Renal function
- Serum levels of interacting drugs (e.g., theophylline, ciclosporin)
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.