Page 983 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

958 CHAPTER 7

VetBooks.ir Samples should be submitted as soon as cantharidin RENAL PHARMACOLOGY
toxicosis is suspected because cantharidin is elimi-
The reader should refer to the specific disease in the
nated within 3–4 days.
text for drug use, drug selection, dose and route of
Management administration.
Treatment is supportive. The source of toxin must
be removed. Potentially exposed animals should be Beta-lactam antibiotics
treated orally with mineral oil (4–6 litres via naso- Penicillins are often used in the urinary tract because
gastric tube) or activated charcoal (1–3 g/kg via they possess a number of beneficial properties. They
nasogastric tube). Mineral oil acts as a mild laxative are bactericidal, have a wide margin of safety and a
and absorbs lipid-soluble cantharidin, which aids in relatively low incidence of adverse effects, and many
the elimination of cantharidin from the intestine. achieve very high levels in urine because of renal
Mineral oil and activated charcoal should not be excretion. Microorganisms that are reported to be
administered concurrently. resistant in vitro are often, in fact, sensitive in vivo
Intravenous balanced electrolyte solution admin- because of the high drug concentrations that may
istration (120–180 ml/kg/day) should be com- be achieved in urine, particularly alkaline urine.
menced. Administration of diuretics (furosemide Acidification of the urine may affect the pharmaco-
1 mg/kg i/v or i/m q6 h) has been recommended kinetic variables of penicillin. Intravenous adminis-
to increase cantharidin excretion after the patient tration of ampicillin, however, can be combined with
is rehydrated. Supplementation of i/v fluids with urinary acidifiers.
calcium borogluconate may be required and is ide- Cephalosporins have the same mechanism of
ally based on repeated evaluation of serum ionised action as penicillins and also achieve very high con-
calcium level. Magnesium supplementation is less centrations in urine. In general, cephalosporins have
commonly required but can be achieved by admin- a broader spectrum with enhanced gram-negative
istration of magnesium sulphate (0.2–1.0 g/kg dis- activity compared with penicillins. Both penicillins
solved in 4 litres of warm water q12 h). and cephalosporins are effective against most anaer-
Analgesics are usually required and should be obes. Penicillins and cephalosporins rarely cause
administrated sparingly. NSAIDs should be avoided renal tubular damage and renal disease.
if possible or given at reduced doses (flunixin meglu-
mine ≤0.5 mg/kg i/v q12 h; ketoprofen ≤1.1 mg/ Sulphonamides
kg i/v or i/m q24 h) and only after hypovolaemia is Sulphonamides are typically used in combination
corrected with i/v fluid therapy. Alpha-2 agonists with trimethoprim, which provides broad-spectrum
and opioids are good alternatives for short-term bactericidal activity. They are eliminated by a com-
analgesia. bination of renal excretion and metabolism in the
Prophylactic treatment with appropriate antibiot- liver. The trimethoprim/sulphadiazine combination
ics to prevent the development of secondary cystitis is more suitable for treatment of urinary tract infec-
has been recommended but may not be necessary in tion than trimethoprim/sulphamethoxazole; sulpha-
most cases. If antimicrobials are used, nephrotoxic methoxazole is largely metabolised before urinary
drugs should be avoided. excretion. Alkaline urine improves the solubility
of sulphonamides after they undergo acetylisation.
Prognosis They should not be given in combination with urine
The prognosis is variable and depends on the amount acidifiers. Crystalluria, haematuria and obstruction
of cantharidin that was ingested and the time from of renal tubules, although rare, have been reported
the onset of signs to the start of appropriate treat- after administration of sulphonamides. Acidic urine
ment. Laminitis has occasionally been associated and dehydration may predispose to the development
with cantharidin toxicosis. of the above problems.