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Clarithromycin is one of the newer macrolide antibiotics. Like other macrolide antibiotics, clarithromycin is generally bacteriostatic and works by inhibiting protein synthesis within susceptible bacteria. Clarithromycin is well absorbed orally. Macrolide antibiotics are not used in horses greater than one year of age due to severe, potentially fatal colitis.
Rifampin is either a bacteriostatic or bactericidal
antibiotic that inhibits DNA-dependant RNA polymerase in susceptible bacteria.
It is well-absorbed from the GI tract and penetrates many bodily tissues,
including the cerebral-spinal fluid. Rifampin is combined with other antibiotics
in the treatment of difficult walled-off infections because it increases
the penetration of antibiotics into abscesses. It is always used in combination
with other antibiotics because resistance develops rapidly when it is
used alone. Rifampin is highly protein-bound and is metabolized by the
liver.
Clarithromycin combined with rifampin is used in foals primarily for the treatment R.equi infection. For many years erythromycin combined with rifampin was the standard of care in the treatment of R.equi infections. Recently, the newer advanced generation macrolides, such as clarithromycin and azithromycin, have gained popularity due to their better absorption and penetration characteristics. Research indicates that clarithromycin concentrates in pulmonary epithelial lining fluid (PELF) and in bronchial alveolar (BAL) cells of foals. Antibiotic levels for oral clarithromycin exceed the minimum inhibitory concentration in the PELF and BAL for a full twelve hours. Research performed by Giguere at the University of Florida concluded that foals treated with the combination of clarithromycin and rifampin exhibited significantly better radiographic improvement and, overall, had better short-term and long-term treatment success when compared to those treated with azithromycin/rifampin or erythromycin/rifampin combination. The treatment success rate for foals with severe radiographic lesions was greater than 80 percent.
Clarithromycin combined with rifampin may be used for
the treatment of Lawsonia intracellularis in foals. Older horses
are generally treated with either tetracyclines, chloramphenicol, metronidazole
or other antibiotics.
The most common side effects in all species are gastrointestinal.
Mild to moderate diarrhea may occur in foals. Hyperthermia is a serious
and potentially fatal side effect that may be seen in foals. There is
ample clinical evidence that foals on erythromycin are very sensitive
to heat and possibly to bright sunlight and there have been anecdotal
reports of similar hyperthermia with both clarithromycin and azithromycin.
Because of this problem, many veterinarians do not turn foals on macrolide
antibiotics out in the daytime, and may severely limit their turnout time
in general. Should hyperthermia occur, aggressive cooling using water
and fans or air-conditioning is helpful.
• Clarithromycin/rifampin should be used with caution
in animals with decreased liver function.
• Macrolide antibiotics are not used in horses one year of age or
older due to severe, potentially fatal diarrhea. Severe diarrhea has also
been reported in mares whose suckling foals are on erythromycin. Extra
care should be used to minimize or prevent any exposure to the mare from
macrolide antibiotics. Water buckets and the foal's skin are potential
sources of exposure.
• Rifampin is always used in combination with other antibiotics,
as resistance will develop if used as mono-therapy. Rifampin may cause
a harmless red/orange discoloration of urine, tears or sweat.
• Clarithromycin has a number of potential drug interactions when
used in animals other than foals with R. equi infections. If using
this drug in other species, other drug interactions may occur.
• In foals, interaction of omeprazole and clarithromycin may increase
levels of each drug.
• Rifampin induces the liver microsomal enzymes. The metabolism of
the following drugs may hypothetically be affected: barbiturates, benzodiazepine
and corticosteroids.
• Overdose of any macrolide antibiotic can cause severe GI side
effects.
• Some veterinarians use oral probiotics in foals being treated with
macrolide antibiotics in an attempt to decrease the likelihood or severity
of antibiotic induced diarrhea.
Dr.
Barbara Forney is a veterinary practitioner in Chester County, Pennsylvania.
She has a master's degree in animal science from the University of Delaware
and graduated from the University of Pennsylvania School of Veterinary Medicine
in 1982.
She began to develop her interest in client education and medical writing 1997. Recent publications include portions of The Pill Book Guide to Medication for Your Dog and Cat, and most recently Understanding Equine Medications published by the Bloodhorse.
Dr. Forney is an FEI veterinarian and an active member of the AAEP, AVMA, and AMWA.
You can purchase books by Dr. Forney at www.exclusivelyequine.com
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risks and benefits of using a particular product. You should consult your doctor
about diagnosis and treatment of any health problems. Information and statements
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