Erythromycin: veterinary dose and monograph

At a glance

Drug class

Antibiotic

Also known as

Erythrocin, Althrocin, Erythromycin estolate/ethylsuccinate

Species with doses

Dogs, Cats, Cattle, Horses, Sheep, Pigs, Birds and Ferrets

General dose range

10–20 mg/kg PO q8–12h — check the species tables for the indication

Routes

PO, IV, IM

Last reviewed

1 October 2026

Indications

• Susceptible Gram-positive infections (Staphylococcus, Streptococcus)
• Campylobacter enteritis
• Rhodococcus equi pneumonia in foals (with rifampin)
• Mycoplasma / respiratory infection
• GI prokinetic at low (sub-antibacterial) doses for delayed gastric emptying / ileus

Erythromycin dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Dogs

• Susceptible infection: Papich 5e: 10–20 mg/kg q8–12h PO. Plumb’s p.482: 10–20 mg/kg PO three times daily (Aucoin 2000); soft tissue 10–15 mg/kg q8h or 15–25 mg/kg q12h for 7–10 days; systemic 22 mg/kg PO or IV q8h. Vomiting is the commonest side effect.
• GI prokinetic (delayed gastric emptying): Papich 5e: 0.5–1 mg/kg q8–12h PO or IV. Plumb’s p.482: 0.5–1 mg/kg PO q8h (Hall & Washabau; Twedt 2008) — sub-antimicrobial motilin-receptor effect.

Cats

• Susceptible infection: Papich 5e: 10–20 mg/kg q8–12h PO. Plumb’s p.482: 10–20 mg/kg PO three times daily; prokinetic 0.5–1 mg/kg PO q8h.

Cattle

• Susceptible infection: Plumb’s p.482: 4–8 mg/kg IM q12–24h (Jenkins 1987); label withdrawal cattle 14 days slaughter, 72 h milk. Papich 5e: abscesses/pododermatitis 2.2–8.8 mg/kg q24h IM; pneumonia up to 15 mg/kg q12h IM. High-dose Erythro-200 44 mg/kg IM q24h needs a 30-day withdrawal (Hjerpe 1986). Injection-site reactions.

Horses

• Rhodococcus equi pneumonia (FOALS only, with rifampin): Foals only. Papich 5e: phosphate or estolate 37.5 mg/kg q12h or 25 mg/kg q8h PO (the plain base is poorly absorbed). Plumb’s p.482: 20–25 mg/kg PO q6–8h (Haggett & Wilson 2008); 25 mg/kg q12h with rifampin 3–5 mg/kg q12h for 4–6 weeks (Foreman); Lawsonia 25 mg/kg q6–8h with rifampin for ≥21 days. Mares exposed to faeces of treated foals, and adult horses, can develop fatal colitis; foals may develop hyperthermia.
• GI prokinetic (lactobionate IV): Papich 5e: erythromycin lactobionate 1 mg/kg to stimulate GI motility (antimicrobial IV dose 5 mg/kg q4–6h). Colitis risk in adult horses.

Goats

• No reference dose for this species: Neither Papich 5e nor Plumb’s gives an erythromycin dose for goats (Plumb’s lists sheep only).

Sheep

• Respiratory infection (label): Plumb’s p.482 (label): sheep 2.2 mg/kg IM once daily for respiratory infections; slaughter withdrawal 3 days, milk 72 h. Newborn-lamb dysentery prevention: 123 mg/kg IM once soon after birth (label).

Pigs

• Respiratory / susceptible infection: Plumb’s p.482 (label): respiratory infections 2.2–6.6 mg/kg IM once daily; scours in young pigs 22 mg/kg IM daily; slaughter withdrawal 7 days.

Buffalo

No buffalo-specific doses are on file, so buffalo are dosed as cattle.

• Susceptible infection: Plumb’s p.482: 4–8 mg/kg IM q12–24h (Jenkins 1987); label withdrawal cattle 14 days slaughter, 72 h milk. Papich 5e: abscesses/pododermatitis 2.2–8.8 mg/kg q24h IM; pneumonia up to 15 mg/kg q12h IM. High-dose Erythro-200 44 mg/kg IM q24h needs a 30-day withdrawal (Hjerpe 1986). Injection-site reactions.

Birds

• Susceptible infection (respiratory): Plumb’s p.482 (Hoeffer 1995): oral suspension 60 mg/kg PO q12h; ratites 5–10 mg/kg PO three times daily (Jenson 1998).

Rabbits

• Not recommended: Papich 5e: in rodents and rabbits the diarrhoea caused by erythromycin can be serious and even fatal.

Ferrets

• Susceptible infection: Plumb’s p.482 (Williams 2000): 10 mg/kg PO four times daily.

Contraindications

Adult horses and other hindgut fermenters — high risk of fatal antibiotic-associated colitis (Clostridioides difficile). Macrolide hypersensitivity. Hepatic dysfunction (estolate salt is hepatotoxic). Concurrent drugs heavily metabolised by CYP3A (potent inhibitor).

Species-specific warnings

Horses: Use ONLY in foals (Rhodococcus). In adult horses it causes fatal antibiotic-associated colitis. Even foal treatment can cause hyperthermia and colitis in the dam/foal.

Rabbits: Do not give to rabbits — fatal enterotoxaemia.

Small mammals: Avoid in guinea pigs, chinchillas, hamsters — fatal dysbiosis.

Adverse effects

• GI: vomiting, abdominal cramping, diarrhoea (motilin agonism)
• Fatal colitis in adult horses / hindgut fermenters
• Hepatotoxicity (cholestatic, mainly estolate)
• Thrombophlebitis (IV), pain on IM injection
• QT prolongation at high doses

Drug interactions

• Potent CYP3A4 inhibitor: raises levels of cisapride, cyclosporine, digoxin, theophylline, midazolam, ketoconazole — toxicity risk
• Other QT-prolonging drugs: additive arrhythmia risk
• Statins: increased myopathy risk
• Antagonism with bactericidal cell-wall agents (theoretical)
• Antacids reduce absorption of some salts

Pregnancy and lactation

Generally considered acceptable in pregnancy (one of the safer antibiotics); estolate salt avoided due to maternal hepatotoxicity. Enters milk.

Monitoring

• GI tolerance (vomiting/diarrhoea) — dose-limiting
• Liver enzymes on prolonged therapy / estolate salt
• Levels/effects of interacting CYP3A drugs
• Foal colitis surveillance during Rhodococcus protocols (and dam — exposure via foal handling)

Toxicity and overdose

Main acute hazard is GI — severe vomiting/cramping from motilin agonism, and in adult horses/hindgut fermenters, life-threatening colitis. Chronic/high dose: cholestatic hepatotoxicity (estolate), QT prolongation. Overdose is rarely lethal in monogastric small animals beyond severe GI signs.

Management: No specific antidote. Supportive — fluids, anti-emetic, manage GI signs. Discontinue and treat colitis aggressively (fluids, anti-endotoxic care) if it occurs in equids. ECG if very high doses. Hepatoprotection if estolate hepatotoxicity.

Clinical pearls

• Low-dose erythromycin (0.5–1 mg/kg) is a useful GI prokinetic — distinct from its antibacterial dose
• With rifampin, it remains a classic regimen for Rhodococcus equi pneumonia in foals
• Absolutely avoid in adult horses, rabbits, guinea pigs and other hindgut fermenters — fatal colitis
• Remember it is a strong CYP3A inhibitor — review co-medications (notably cisapride, cyclosporine, theophylline)
• GI cramping is the commonest reason owners stop the drug — warn them and consider divided/with-food dosing

Mechanism of action

Macrolide that binds reversibly to the 50S ribosomal subunit (23S rRNA), blocking the translocation step of bacterial protein synthesis — predominantly bacteriostatic, time-dependent. Separately, it directly stimulates motilin receptors on GI smooth muscle, producing dose-dependent prokinetic contractions at sub-antimicrobial doses.

Formulations and products

• 250 mg tablet
• 500 mg tablet
• Oral suspension 25 mg/mL (125 mg/5 mL)
• Oral suspension 50 mg/mL (250 mg/5 mL)
• Erythromycin vet oral/inj (Various (India)) — Erythromycin, Tablet / injection
• Erythrocin — 250 / 500 mg tablet; 125 mg/5 mL suspension, Tablet / suspension (human-label)
• Althrocin — 100 / 250 / 500 mg; suspension, Tablet / suspension / drops (human-label)

Storage

Tablets/capsules: 15–30 °C, dry. Oral suspension: refrigerate per label and shake; discard after labelled period. Protect from light.

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

Other antibiotics

• Colistin (Polymyxin E)
• Danofloxacin
• Doxycycline
• Enrofloxacin
• Florfenicol
• Fusidic Acid
• Gamithromycin
• Gentamicin

Frequently asked questions