By Wendy C. Brooks, DVM, DipABVP
Educational Director, VeterinaryPartner.com
Brand Name: Chloromycetin (Abbreviated As CHPC)
Available in 50 mg, 100 mg, 250 mg, 500 mg and 1 gram capsules/tablets; oral suspension (liquid); assorted eye and ear formulations
History And Background
Since the development of penicillin and sulfa drugs, the first commercially produced antibiotics, we have sought to improve upon our ability to combat bacteria. We want medications that:
- Can be given orally so that medical treatment can be given at home
- Do not affect the normal bacterial residents of the body adversely
- Have minimal side effects
- Are able to penetrate through infected tissue (pus) or through natural barriers of the body where infection may be sequestered (such as within the eye, nervous system or prostate gland).
Chloramphenicol represents the product of years of antibiotic development. Due to its pH, it shines above most other antibiotics in terms of ability to penetrate into infected tissues and tissues with biological barriers. Chloramphenicol can easily pass deeply through purulent material (pus) to the organisms hiding within, through cell membranes to attack parasites living within, and into organs where other antibiotics cannot go.
Chloramphenicol acts on the protein manufacturing system of bacteria (the cell's ribosomes) yet does not affect mammalian, reptilian, or avian ribosomes. With protein manufacture being highly crucial for metabolism, disrupting a cell's ability to make protein is disastrous. Highly susceptible bacteria are killed outright while others are merely rendered unable to divide and the host's immune system then destroys them upon discovery. Chloramphenicol has an especially broad spectrum of activity against numerous aerobic bacteria, mycoplasma, chlamydial organisms, and anaerobic bacteria.
How This Medicine Is Used
Chloramphenicol may be given orally or topically, usually three times daily. Peak activity occurs approximately 30 minutes after an oral dose except in the nervous system where several hours are required to penetrate the blood/brain barrier. This medication is an especially good choice for infections where:
- There is a necrotic or walled off area with inner infection (pneumonia is a good example)
- The central nervous system or eye is involved
- The prostate gland is involved
- Intracellular parasites are involved (chlamydia, mycoplasma, rickettsia).
Unfortunately, chloramphenicol must typically be given three times daily for dogs. This schedule is relatively inconvenient for most pet owners and probably accounts for this drug falling from favor, replaced by products that can be used twice or even once a day. Cats have some sensitivity issues with this medication (see below), thus it has never been a common feline treatment.
Aside from its uses for obvious infection, chloramphenicol has been used for the musculoskeletal disease called hypertrophic osteodystrophy, or HOD. This is a condition of adolescent large or giant breed dogs where they develop painful areas near the growth plates of their long bones. This treatment is of some controversy as the cause of HOD has not been clearly shown to be bacterial and it is does eventually resolve on its own. (In other words, any role of chloramphenicol in treating this condition is difficult to evaluate.)
In some individuals, chloramphenicol use may induce what are called blood dyscrasias. This means that abnormal blood cells can be produced or that production of normal cells can be halted due to an action of chloramphenicol on patient bone marrow. This reaction is especially of concern in cats and chloramphenicol should be used with caution in this species (special dosing, perhaps even some blood monitoring).
Chloramphenicol use may accumulate to toxic levels in very young animals (in the first few weeks of life) and as they are not able to remove it from their bodies as effectively as adult animals. For this reason, it is best not to give this medication during pregnancy or lactation.
Nausea, diarrhea, and appetite loss are relatively common (and usually minor) side effects of this medication but if they occur, another medication can be selected.
Interactions With Other Drugs
The following drugs may last longer than expected if used concurrently with chloramphenicol:
- Phenytoin (used for both heart disease and for seizures)
- Primidone (used for seizures)
- Phenobarbital (used for seizures)
- Cyclophosphamide (used in chemotherapy)
- Opiate pain relievers
The use of the following drugs may interfere with the activity of chloramphenicol:
Cimetidine, an antacid, may interfere with the body's removal of chloramphenicol, which could increase the potential for toxicity.
Concerns And Cautions
Three times a day dosing is inconvenient for most pet owners and often doses are missed. Be aware that in many cases other antibiotics that can be given twice daily could be substituted. If you know that three times daily administration is not likely to be performed reliably, let your veterinarian know.
Chloramphenicol powder reportedly tastes terrible and may not be accepted if tablets are crushed and mixed with food.
Chloramphenicol should not be used in patients with abnormal bone marrow, non-regenerative anemia, or circulating abnormal blood cells.
Chloramphenicol is removed from the body via the liver's detoxification mechanisms. If a patient is in liver or kidney failure, some other antibiotic is probably a better choice.
Chloramphenicol should not be used in breeding animals or in pregnant females or in newborns.
Vaccinations should not be given during a course of chloramphenicol.
Humans may develop fatal aplastic anemia if exposed orally (through the mouth) to chloramphenicol; the risk is approximately one person in 25,000. This condition is irreversible and is not dependent upon dosages. For this reason, chloramphenicol has been banned from food animal use in the United States as well as from human use. Washing hands after handling this medication is recommended.
It is our policy not to give dosing information over the Internet.