Ery-Tab, Mycin, Robimycin, Robitabs, Eryc, EryPed, EryPed drops.


  • Tablets: 250 mg, 500 mg
  • Capsules: 250 mg, 500 mg
  • Suspensions: range variety from 5 mg/mL, 250 mg/mL to 200 mg/5mL, 400 mg/5 mL

*Note: Ornacyn sold over counter for birds in pet store. Note: however, that although some birdbiotics and fishbiotics may be used in emergencies by pet rat owners, it is not recommended to do so. Compounding to dose for accuracy may be difficult depending on how they are distributed. For example, whether they are sold as powder form, as a capsule or as a tablet. In addition, since these products are not federally regulated, they may not be of the same quality and purity as those administered by prescription. It is recommended to always seek the advice of a qualified veterinarian regarding treatment of an ill rat.


Erythromycin, a macrolide, bacteriostatic, antibiotic is believed to inhibit bacterial protein synthesis by binding to the ribosomal 50S subunit. It is used in the treatment against Gram-positive bacilli such as, Bacillus anthracis, corynebacterium, clostridium, and the Gram-positive cocci, staphylococcus and streptococcus, as well as some strains of mycoplasma.
At high concentrations or against highly susceptible organisms’ erythromycin may act as a bactericidal.

Erythromycin is absorbed in the upper small intestine after given orally. It is widely distributed throughout most body fluids and tissues with the exception of a lesser amount in cerebral spinal fluid. It crosses the placental barrier and appears in breast milk.

In some 2-year studies, in rats, it has shown no observable teratogenic or carcinogenic effects at greater than the human dose.
In other studies, it was shown that at similar doses there may be decreased contractility of the uterus in the pregnant rat. *Note: dosages used in both studies were at greater than the therapeutic range for the rat (see references to studies listed below).
Based on animal studies, erythromycin is believed to be safe for use during pregnancy and lactation, at therapeutic doses.

Erythromycin is metabolized partially in the liver and excreted in bile along with a small amount in urine.


Can be used in mild respiratory infections.

Clinical Pearl

Erythromycin can cause stomach upset. Give with food.

Drug Interactions or Contraindications

  • Chloramphenicol and lincosamides are antagonists of erythromycin, they should not be used concurrently.
  • Not recommended to be used concurrently with other macrolides.
  • Erythromycin may increase digoxin’s absorption in the GI tract if used concurrently.
  • Cisapride metabolism is inhibited by erythromycin. Avoid concurrent use.
  • Erythromycin may interfere with the metabolism of the following drugs. IF using concurrently dosing of those medications may need to be adjusted:
    • Bromocriptine
    • Methylprednisolone
    • Theophylline
    • Ketoconazole

Adverse Reactions

GI: anorexia, diarrhea

Skin:  itching

Other: pain at injection site

Dosage Recommendations

5 mg/lb to 10 mg/lb , PO , TID  4
If choosing to use ornacyn, 1/2 to 1 tablet in 2 oz. water mixed daily; or 1/8 tablet in food TID  4
(Give med for at least 14 days)


10 mg/kg, PO, q24hr (Chronic respiratory disease, rats) 41, 44


20 mg/kg, PO, q12hr  1, 34, 35, 41, 42, 44


  • Considered safe, it is still wise to consult with a vet if you think your rat is pregnant or if your rat is nursing.
  • If mixing med in water, reduce moist food to encourage rat to drink.
  • Store capsules and tablets at room temperature.
  • Solutions and suspensions should be refrigerated. However, some individual oral suspension products are stable for 14 days at room temperature. Check with veterinarian or pharmacist.

  1. Erythromycin – Erythromycin Thiocyante – Erythromycin Stearate: Summary Report 1. (n.d.). Retrieved December 12, 2008, from
  2. Erythromycin. (1995, July 25). Retrieved December 12, 2008, from
  3. Granovsky-Grisaru, S., Ilan, D., Grisaru, D., Lavie, O., Aboulafia, I., Diamant, Y., & Hanani, M. (1998). Effects of erythromycin on contractility of isolated myometrium from pregnant rats. Am J Obstet Gynecol, 178(1 pt 1), 171-4. Retrieved December 12, 2008, from
    Gerald G. Briggs, B.Pharm. — Archived page from 2005-03-11 (via the Wayback Machine)


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