Erythromycin
Also known as: Ilotycin · Erythrocin · Erythroped · Erythromycinum
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Audited v13 dosing evidence
Structured calculator evidenceProkinetic agent (extra-label)
Verified clinician required
- q8h
NA
Governing clinical context (4)
- NOTE: IV injections should be given slowly (ie, over 20-60 minutes). See Adverse Effects.
- Erythromycin (base) capsules and tablets should be stored in airtight containers at room temperature of 15°C to 30°C (59°F-86°F).
- Erythromycin ethylsuccinate tablets and powder for oral suspension should be stored in airtight containers at room temperature.
- Erythromycin lactobionate powder for injection should be stored at room temperature. For initial reconstitution (vials), use only sterile water for injection. After reconstitution, the drug is stable for 24 hours at room temperature and for 2 weeks if refrigerated. To prepare for administration via continuous or intermittent infusion, the drug is further diluted in 0.9% sodium chloride, lactated Ringer’s solution, or Normosol®-R. Other infusion solutions may be used but first must be buffered with 4% sodium bicarbonate injection (1 mL per 100 mL of solution). At a pH of less than 5.5, the drug is unstable and loses potency rapidly.
Susceptible infections (extra-label)
- q8-12h
NA
Governing clinical context (3)
- Erythromycin (base) capsules and tablets should be stored in airtight containers at room temperature of 15°C to 30°C (59°F-86°F).
- Erythromycin ethylsuccinate tablets and powder for oral suspension should be stored in airtight containers at room temperature.
- NOTE: IV injections should be given slowly (ie, over 20-60 minutes). See Adverse Effects.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
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 of action
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.
Safety & warnings
Contraindications
- Hepatic dysfunction (especially the estolate salt)
Adverse effects
- Gastrointestinal upset (most common)
- Cholestatic hepatitis (associated with estolate salt in humans)
Drug interactions
May enhance the absorption of digoxin from the GI tract
Increases serum levels of ciclosporin
Increases serum levels of cisapride, leading to potentially fatal arrhythmias
Increases serum levels of methylprednisolone
Increases serum levels of theophylline
Increases serum levels of terfenadine, leading to potentially fatal arrhythmias
Antagonism may occur if used in combination
Antagonism may occur if used in combination
Antagonism may occur if used in combination (competes for 50S binding site)
Monitoring
- Gastrointestinal signs
- Hepatic function (especially if using estolate salt)
- Renal function
- Serum levels of interacting drugs (e.g., theophylline, ciclosporin)
Pharmacokinetics
Absorption
The base is acid-labile and should be administered on an empty stomach.
Distribution
Being a lipophilic weak base, it is concentrated in fluids that are more acidic than plasma, including milk, prostatic fluid, and intracellular fluid.
Available products
Formulations
- Ophthalmic ointment 0.5%
- 250 mg tablet
- 500 mg tablet
- 250 mg capsule
- 500 mg capsule
- 250 mg/5ml oral suspension
Human-labeled
- Erythromycin 0.5% ophthalmic ointment, 3.5 gram tube, generic (Rx)
- Erythrocin
- Erythroped
- Erythromycin 250 mg tablets/capsules
- Erythromycin 500 mg tablets/capsules
- Erythromycin 250 mg/5ml suspension
Regulatory status
POM-V, POM
POM-V, POM
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Client information
Important: This medication is for ophthalmic (eye) use only.
- Administration: Apply a ½ inch strip of the ointment to the affected eye(s) 3 to 4 times daily, as directed by your veterinarian.
- Hygiene: Wash your hands before and after application. Do not let the tip of the tube touch the eye, eyelids, or any other surface to prevent contamination.
- Consistency: Complete the entire course of treatment even if the eye looks better, to prevent the infection from returning or developing resistance.
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.