# Erythromycin: veterinary dose and monograph

> Erythromycin is a veterinary antibiotic. Prototype macrolide antibiotic — bacteriostatic against Gram-positive cocci, some Gram-negatives, Mycoplasma and Campylobacter. Indications include susceptible Gram-positive infections (Staphylococcus, Streptococcus); campylobacter enteritis; rhodococcus equi pneumonia in foals (with rifampin). This monograph lists 10 reference doses for dogs, cats, cattle, horses, sheep and pigs and 2 more species, each with route, frequency and source, plus meat and milk withdrawal periods for food animals.

Source: https://vetmasterji.com/drugs/erythromycin · Last reviewed: 2026-10-01

## 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

*Erythromycin doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Susceptible infection | 10–20 mg/kg | PO | q8–12h | — |
| GI prokinetic (delayed gastric emptying) | 0.5–1 mg/kg | PO | q8h | — |

- 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

*Erythromycin doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Susceptible infection | 10–20 mg/kg | PO | q8–12h | — |

- 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

*Erythromycin doses for cattle*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| Susceptible infection | 4–8 mg/kg | IM | q12–24h | — | 14d slaughter |

- 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

*Erythromycin doses for horses*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Rhodococcus equi pneumonia (FOALS only, with rifampin) | 25 mg/kg | PO | q6–8h | 4–8 weeks |
| GI prokinetic (lactobionate IV) | 1 mg/kg | IV | as needed | — |

- 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

*Erythromycin doses for goats*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| No reference dose for this species | Not established in Papich 5e or Plumb’s 10e — do not extrapolate from another species | — | — | — | — |

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

### Sheep

*Erythromycin doses for sheep*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| Respiratory infection (label) | 2.2 mg/kg | IM | q24h | — | 3d slaughter / 72h milk |

- 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

*Erythromycin doses for pigs*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| Respiratory / susceptible infection | 2.2–6.6 mg/kg | IM | q24h | — | 7d slaughter |

- 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.

*Erythromycin doses for buffalo*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| Susceptible infection | 4–8 mg/kg | IM | q12–24h | — | 14d slaughter |

- 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

*Erythromycin doses for birds*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Susceptible infection (respiratory) | 60 mg/kg | PO | q12h | — |

- 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

*Erythromycin doses for rabbits*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Not recommended | Avoid in rabbits and rodents — diarrhoea can be severe or fatal | — | — | — |

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

### Ferrets

*Erythromycin doses for ferrets*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Susceptible infection | 10 mg/kg | PO | q6h | — |

- 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

> **Caution:** 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.

> **Caution:** Rabbits: Do not give to rabbits — fatal enterotoxaemia.

> **Caution:** 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

> **Caution:** 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.

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## Frequently asked questions

### What is the dose of Erythromycin for dogs?

Reference doses for Erythromycin in dogs: 10–20 mg/kg PO q8–12h (Susceptible infection); 0.5–1 mg/kg PO q8h (GI prokinetic (delayed gastric emptying)). Confirm against the label and the patient before use.

### What is the dose of Erythromycin for cats?

Reference doses for Erythromycin in cats: 10–20 mg/kg PO q8–12h (Susceptible infection). Confirm against the label and the patient before use.

### What is the dose of Erythromycin for cattle?

Reference doses for Erythromycin in cattle: 4–8 mg/kg IM q12–24h (Susceptible infection). Confirm against the label and the patient before use.

### What is the withdrawal period for Erythromycin?

Cattle, IM (Susceptible infection): 14d slaughter; Sheep, IM (Respiratory infection (label)): 3d slaughter / 72h milk; Pigs, IM (Respiratory / susceptible infection): 7d slaughter. Follow the product label and national regulations where they differ.

### When should Erythromycin not be used?

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).

### What are the side effects of Erythromycin in animals?

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.

## Sources

- Plumb's Veterinary Drug Handbook
- Merck Veterinary Manual, 11th edition
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.