| Antibiotic/Antifungal/Antiviral
Therapy
Please scroll down for more information on the
following topics:
Metronidazole
Esophageal Strictures Secondary to Administration
of Doxycycline Tablets
Oral Itraconazole for Therapy of Dermatophytosis
Caused by Microsporum canis
Chloramphenicol Suspension for Birds & Small
Animals
Fluoroquinolone Antibiotics
Antibiotic Treats for Feline Abscess
Intranasal Clotrimazole for Treatment of Nasal
Aspergillosis in Dogs
Azithromycin
Azithromycin for R. equi Infections in Foals
Idoxuridine Ophthalmic Drops for Cats
Feline Ocular Toxoplasmosis
Itraconazole/DMSO for Fungal Keratitis in Horses
Metronidazole
Metronidazole is effective against a variety of
obligate anaerobic bacteria as well as anaerobic
protozoa such as Giardia and Trichomonas. “Various
salts of metronidazole with improved palatability
are now available for veterinary patients... Cats
and birds accept the benzoate salt much more willingly
than they accept metronidazole HCl and do not
seem to be stressed by its administration.”
Metronidazole should be used with caution in patients
with hepatic dysfunction. Therapy should be promptly
discontinued if abnormal neurological signs appear,
including nystagmus, ataxia, seizures, and rigidity.
All benzene moieties must be conjugated with glucuronide
to facilitate elimination and this pathway is
inefficient in cats. Therefore, doses of metronidazole
benzoate above 200 mg/kg/day may produce signs
of cumulative toxicity in cats within 48 to 72
hours.
Compendium Dec. 2000: 22(12); pp. 1104,
1105, 1107, 1130
Esophageal Strictures Secondary to Administration
of Doxycycline Tablets
“The most common causes of esophageal strictures
in dogs and cats are gastroesophageal reflux during
anesthesia, persistent vomiting, or ingestion
of foreign bodies or caustic agents. In humans,
esophageal retention of oral medication is a common
cause of severe esophagitis. Of the medications
proven to lead to esophageal ulceration, doxycycline
is most often implicated. It has been suggested
that pill-induced esophagitis also could occur
in small animals...” Drug-induced esophageal
ulceration usually occurs when tablets are taken
with little or no water and adhere to the esophageal
mucosa. Once this occurs, flushing with large
quantities of liquid fails to wash the medication
into the stomach. Melendez et al. of Colorado
State University College of Veterinary Medicine
report on three cases of presumptive doxycycline-induced
esophagitis in cats, with resultant stricture
formation. All cats had been administered fractions
of doxycycline tablets one to three weeks before
presenting with a chief complaint of regurgitation.
“Two of the cases developed regurgitation
within 7 days after initiation of therapy with
doxycycline. One cat, which was treated while
at an animal shelter, was noted to be regurgitating
the day that it was adopted, approximately 2 weeks
after being treated with doxycycline. No other
cause of esophageal stricture formation could
be identified.” If a pet that has received
a doxycycline tablet shows sign of esophagitis
(dysphagia, excessive salivation, inappetence,
and regurgitation), the doxycycline tablets should
be discontinued. Suggested therapy for esophagitis
includes sucralfate slurries, a prokinetic agent
(i.e. cisapride) to increase lower esophageal
sphincter tone, and anti-inflammatory doses of
glucocorticoids to prevent stricture formation.
Feline Practice 28:2; 10-12 (Mar/Apr
2000)
Doxycycline can be compounded as a stable flavored
liquid preparation or other palatable dosage form
to meet the specific needs of each animal and
owner.
Oral Itraconazole for Therapy of Dermatophytosis
Caused by Microsporum canis
Itraconazole could be an effective alternative
to griseofulvin that has toxic effects (particularly
in puppies based on this author’s experience)
and frequent therapeutic relapses. Itraconazole
has also been used to successfully treat M. canis
infection of cats and guinea pigs.
J Am Vet Med Assoc 1998;213:993-995
Chloramphenicol Suspension
for Birds & Small Animals
by J. Terry McGrath, VMD, Pennsylvania
Since chloramphenicol palmitate
is no longer commercially available, we contacted
our compounding pharmacist for an alternative
for use in our avian and other small patients,
such as rabbits and rodents. The pharmacist prepared
a cola flavored suspension containing 30 mg/ml
of chloramphenicol palmitate, which could be administered
using a small oral syringe. However, birds did
not like the taste and it was reformulated into
a tutti fruitti and pina colada syrup. The “animal
appropriate” flavor has really helped with
compliance, because now the birds and small animals
like to take their medicine!
Note: To avoid potential antagonism, chloramphenicol
should not be administered simultaneously with
penicillin or streptomycin. Chloramphenicol-containing
preparations should not be administered in conjunction
with, or two hours prior to, the induction of
general anesthesia with pentobarbital.
When administered orally in dogs, chloramphenicol
is well-tolerated, has high clinical efficacy,
and a low incidence of side effects. The recommended
canine dosage is 25 mg/lb of body weight every
six hours.
Precautions: Chloramphenicol should be administered
cautiously to animals with hematopoietic dysfunction,
or impaired kidney or liver function.
Antibiotic Treats for Feline Abscess
Submitted by: Michael Briggs, Pharm.D. Veterinarian:
Rich Marchetti, D.V.M.
Patient: One year old non-castrated short-haired
male cat with abscess from wound received in fight.
The owner reported that the cat, who is usually
affectionate and friendly toward the owner and
house dog, had been withdrawn, on guard, and growling
for approximately three days. A thorn-like projection
near the tail was found by the owner, who immediately
took the cat to the veterinarian. The cat was
anesthetized and the veterinarian cleaned, debrided,
and shaved the area of the wound, and prescribed
amoxicillin 100 mg daily for ten days. The owner
was instructed to keep the cat inside for the
duration of therapy, to minimize the risk of superinfection
and avoid additional injury.
Medication Problem: The cat refused to take liquids,
and was also resistant to taking tablets (“pilling”).
The required dose of antibiotic was too high for
transdermal treatment (due to the amount of gel
that would need to be applied for each dose).
Solution: The veterinarian called our compounding
pharmacy and asked if we could come up with a
palatable dosage form. We formulated a fish-flavored
chewable treat containing amoxicillin 100 mg to
be given once daily for ten days. This dosage
form offers the advantage of ease of administration,
decreases the potential for dosing errors, and
greatly increases patient compliance. The cat
readily consumed the amoxicillin “treat”.
The wound did not heal in a ten day period, so
five additional days of therapy were required.
Comment: Our pharmacy has compounded this preparation
more than ten times with a 100% success rate.
Intranasal Clotrimazole for Treatment
of Nasal Aspergillosis in Dogs
“Treatment of nasal aspergillosis with systemic
antifungal medications, such as thiabendazole,
ketoconazole, and fluconazole, has been disappointing
because the response rate is only 43 to 60%. Response
to oral administration of itraconazole has been
approximately 60 to 70%... Topical administration
of the imidazoles, enilconazole, and clotrimazole
is more effective than orally administered antifungal
medications.”
Topical administration of clotrimazole resulted
in resolution of clinical disease in 65% of dogs
after 1 treatment and 87% of dogs after one or
more treatments. Topical administration of clotrimazole,
using either technique, was an effective treatment
for nasal aspergillosis in dogs. Use of non-invasive
intranasal infusion of clotrimazole eliminated
the need for surgical trephination of frontal
sinuses in many dogs and was associated with fewer
complications. Nasal discharge ceased in most
dogs 2 weeks after topical treatment, and the
authors now recommend re-treatment with clotrimazole
if nasal discharge has not improved 2 weeks after
treatment.
“[Damage] of the cribriform plate may contraindicate
use of topical treatment; complications arising
from leakage of antifungal medications into the
CNS in dogs with fungal rhinitis have not been
evaluated.”
J Am Vet Med Assoc 1998 Aug 15;213(4):501-6
Click here to access the PubMed abstract of this article.
J Am Anim Hosp Assoc 1998 Nov-Dec;34(6):487-92
Click here to access the PubMed abstract of this article.
Azithromycin
is a form of erythromycin with improved action
against gram-negative organisms, resistance to
acid degradation, improved tissue penetration,
and a prolonged elimination half-life. Azithromycin
shows potential for use in veterinary medicine,
particularly in cats and certain avian and exotic
species.
“Lacking the prokinetic action of erythromycin,
azithromycin appears to cause fewer GI side effects
and is generally well tolerated after oral administration.
Cats appear to tolerate the drug particularly
well... Animals with a history of arrhythmias
should be monitored while receiving the drug.
Some reduction in dose may be warranted in patients
with hepatic or biliary dysfunction, although
no reduction appears necessary in patients with
renal dysfunction.” Please consult our compounding
pharmacist regarding dosing.
Compendium of Continuing Education 23:3
(March 2001), pp. 242-7
Azithromycin for R. equi Infections in
Foals
On the basis of pharmacokinetic values, minimum
inhibitory concentrations of R. equi isolates,
and drug concentrations in pulmonary epithelial
lining fluid (PELF) and bronchoalveolar cells,
a single daily oral dose of 10 mg/kg may be appropriate
for treatment of R. equi infections in foals.
Persistence of high azithromycin concentrations
in PELF and bronchoalveolar cells 48 hours after
discontinuation of administration suggests that
after 5 daily doses, oral administration at 48-hour
intervals may be adequate.
Am J Vet Res 2001 Dec;62(12):1870-5
Click here to access the PubMed abstract of this article.
The Capsule Report, Mixed Practice/Exotic
Edition Jan 2002;15, 10: page 1
Itraconazole/DMSO for Fungal Keratitis
in Horses
Fungal keratitis is a serious complication of
trauma to the eye. Approximately one-half of the
cases of fungal infections have involved the use
of eye ointments containing corticosteroids after
trauma to the globe of the eye.
“Itraconazole is a third generation triazole
that has superior penetration properties and a
wide spectrum of activity. A 1% solution of itraconazole
in a 30% DMSO and petroleum base has been shown
to reach high concentrations within the stroma
of the cornea when administered every 4 to 6 hours.
In general, every 6 hours is suitable for all
but Fusarium sp which requires every 4 hour administration.”
Disease which is rapidly ulcerating “should
also receive treatment that helps block the enzymes
(collagenase) responsible for ulceration. A 5%
acetylcysteine solution and autologous serum in
which 4 mg/ml of EDTA has been added has been
recommended. These need to be instilled hourly
for best effect. The antimicrobial can be added
to the serum.”
This information has been abstracted from an
article by Robert N. Oglesby, DVM, which appears
on his webpage, “The Horseman’s Advisor.”
For more information, references and complete
text, see www.horseadvice.com/sbs/articles/diseases/skin/infectiouskeratitis.aspl
Idoxuridine Ophthalmic Drops for Cats
The ocular signs of feline herpesvirus I (FHV-1)
infection include bilateral conjunctivitis, serous
ocular discharge which may become mucoid or mucopurulent,
and blepharospasm. If corneal involvement is present,
topical antivirals are prescribed. Research indicates
that idoxuridine is effective against FHV-1. Prolonged
contact with the infected tissue is required.
The 0.1% solution must be applied five times daily.
Previously marketed as Stoxil®, the ophthalmic
solution is not commercially available at this
time.
www.eyevet.info/herpes.aspl (Michael Zigler,
DVM, Cert.V.Ophthal)
Am J Vet Res 1989 Jan;50(1):158-60
Feline Ocular Toxoplasmosis
“The anterior uveitis seen in cats with
a positive serum titer to Toxoplasma gondii may
result from immune-mediated mechanisms and not
the presence or replication of the organism itself.
As a result, it is unclear whether systemic antitoxoplasmic
therapy is beneficial in these cases.” Michael
G. Davidson, DVM, of North Carolina State University,
College of Veterinary Medicine reports in Vet
Clin N Amer, Sep 2000, that he “usually
treats cats with ocular lesions and concurrent
systemic findings of toxoplasmosis with systemic
clindamycin (12.5 mg/kg PO twice daily for 14-21
days) and anti-inflammatory therapy. Other sources
recommend clindamycin 10-12.5 mg/kg every 12 hours
for 4 weeks. Oral trimethoprim-sulfonamide combination
therapy (15 mg/kg every 12 hours for 2 to 4 weeks)
can also be used to treat toxoplasmosis but is
less suitable because of potential side effects
caused by folic acid deficiency in cats.2 In T
gondii seropositive cats exhibiting anterior uveitis
alone and with no systemic signs, Dr. Davidson
recommends topical steroids and atropine alone.
If the cat fails to respond to topical therapy
alone within 1-3 weeks, systemic clindamycin should
be added to the treatment regimen. The rationale
for the use of corticosteroids is to suppress
the damaging inflammation in the retina, which
may affect vision. Corticosteroids are typically
administered 1-2 days after antibiotic therapy
has been initiated to allow adequate tissue levels
of the antimicrobial agent to be achieved. [Dr.
Davidson] does not recommend systemic steroids
in cats with suspected ocular toxoplasmosis because
of the risk of exacerbating systemic replication
of T gondii.”1
Swift and aggressive treatment of uveitis is necessary
to avoid such secondary complications as glaucoma,
cataract formation, and retinal degeneration or
detachment.3
1 The Capsule Report 19:10 (Jan 2001), p. 4
2, 3 Compendium of Continuing Education 23:3 (March
2001), pp. 258-66 |
