Riley's antibiotic (chloramphenicol): Handle with care!

Chloramphenicol recrystallized and
photographed under the microscope
by The Molecular Expressions Collection

Kate, a BTB reader, asked about the antibiotic that Riley is getting. It's an interesting question with an equally interesting answer! The drug they prescribed at New Bolton is chloramphenicol. From what I'm hearing it's a pretty good choice for tough to fight infections. According to Veterinary Pharmacology and Therapeutics, it's "a broad-spectrum antibiotic, effective against gram negative and gram positive organisms, aerobic and anaerobic bacteria, and many intercellular organisms." It attains a high level of penetration into tissues, so it's prescribed a lot for treating areas of the body that are traditionally hard to treat -- the eye, central nervous system, the respiratory system, and hopefully bones.

So why isn't everyone using it?
There's a reason you don't see it used more widely -- there are some substantial risks for the humans administering it. If you don't handle it properly, the stuff can mess you up!

• It can cause bone marrow suppresion (damage), which is thankfully reversible. This condition tends to occur at a certain level of exposure or dosage.
  
• In rare cases it can cause irreversible aplastic anemia, with a fatality rate of 70%. A small percentage of people (estimated from 1 in 10,000 to 1 in 45, 000) are thought to be genetically susceptible. This condition is unrelated to dose or duration of exposure.

Because it is so toxic to humans, this drug should not be administered to animals who will be used as food or will produce food (e.g., milk).

Administration
The best practice for handling chloramphenicol is to never let it come into contact with your eyes, skin, mouth, or any body part. I had to sign a form that I had read and understood the risks before they gave me the prescription. Riley's formuation is basically a 25 gram paste tube that is administered two times a day. To administer this thick, fat tube of paste, you...

• wear nitrile gloves (better protection than latex or rubber gloves)
• wear a face mask
• wear a long sleeved garment or apron that you can "peel off" if it gets paste on it
• wipe any excess meds from walls, your horse's lips, and bedding. For permanent surfaces clean with soap and water.
• Double bag any contaminated material, used tubes, etc. before throwing it away.
  

If any paste gets on your skin, you need to wash it off with soap and water and apply a layer of antibiotic ointment.

Riley got his first dose this morning -- in its natural form it's bitter, but apparently they sauce it up for palatability, and the barn manager told me he took it well. Riley's good about worming/tube paste, but this is a lot of paste, twice a day. I'll be suiting up!

RESOURCES

Chloramphenicol Material Safety Data Sheet

Chloramphenicol in Veterinary Pharmacology and Therapeutics

Chloramphenicol in Equine Clinical Pharmacology

Chloramphenicol in Antimicrobial Therapy in Veterinary Medicine

Suit filed over the death of three thoroughbred horses from The Horse Magazine, October 18 2005

Chloramphenicol: The good, the bad, and the beware from Worms and Germs blog

Chloramphenicols from The Veterinary Formulary