Brand Name: Chloromycetin (abbreviated as CHPC)   

Available in 250 mg, 500 mg, and 1 gram capsules/tablets; oral suspension (liquid); assorted eye and ear formulations    

History and Background    

Penicillin and sulfa drugs were the first commercially produced antibiotics. Since then, the goal has been to improve upon the ability to combat bacteria with 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 
• They are able to penetrate through infected tissue (pus) or through the body's natural barriers 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 its 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, anaerobic bacteria, and even methicillin-resistant Staphylococci.

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 nervous system. 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.)

Side Effects   

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, 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)   
• Aspirin
• Opiate pain relievers 
• Glipizide
• Cyclosporine

The use of the following drugs may interfere with the activity of chloramphenicol:   

• Phenobarbital (used to control seizures as noted) 
• Amoxicillin (another antibiotic) 
• Erythromycin (another antibiotic) 
• Clindamycin (another antibiotic) 
• Tylosin (an antidiarrheal antibiotic)    

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 doses are often missed. Be aware that in many cases, other antibiotics that can be given twice daily could be substituted. If you know that three-times-a-day 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 in pregnant females or in newborns.    

Vaccinations should not be given during a course of chloramphenicol.   

If a dose of chloramphenicol is accidentally skipped, do not double up on the next dose. Simply pick up with the next scheduled dose. 

Store pills at room temperature, protected from light.