Page 774 - Small Animal Internal Medicine, 6th Edition

746 PART VI Endocrine Disorders

containing 100 µg DDAVP/mL) is used most commonly in cats with CDI have reported that their pets become accus-
treating CDI in dogs and cats. Administration of medication tomed to receiving eye drops, mentioning eye or conjuncti-
VetBooks.ir to animals via the intranasal route is possible but is not rec- val irritation as an infrequent complication. If PU and PD
recur despite DDAVP therapy, several possibilities should be
ommended. The DDAVP nasal preparation may be trans-
ferred to a sterile eye dropper bottle and drops placed into
administration technique, inadequate dose, outdated or
the conjunctival sac of the dog or cat. Although the solution considered, including problems with owner compliance or
is acidic, ocular irritation rarely occurs. One drop of DDAVP inactivated DDAVP, or development of a concurrent dis-
contains 1.5 to 4 µg of DDAVP, and a dosage of one to four order causing PU and PD. Hyperadrenocorticism is the
drops administered once or twice daily controls signs of CDI primary differential when PU and PD recur despite DDAVP
in most animals. treatment in a dog with CDI.
Because of the expense of DDAVP nasal drops and loss Chlorpropamide, thiazide diuretics, and oral sodium
of DDAVP drops from the conjunctival sac with head chloride restriction have limited efficacy in the treatment of
shaking, blinking, and inadvertent application of excessive NDI. DDAVP may control the clinical signs if administered
amounts, our preference is to initially try oral DDAVP in massive amounts (i.e., five to ten times the amount used
(DDAVP tablets, 0.1 and 0.2 mg) when using response to for the treatment of CDI), but the cost of the drug obviously
DDAVP to establish the diagnosis of CDI and when provid- detracts from the attractiveness of this therapeutic approach.
ing long-term treatment for CDI. Clinical response in Fortunately, therapy for CDI or NDI is not mandatory as
humans is variable, in part because the bioavailability of oral long as the dog or cat has unlimited access to water and is
DDAVP is approximately 5% to 15% of the intranasal dose housed in an environment that cannot be damaged by severe
in humans. Similar information is not available for dogs and PU. A constant water supply is of paramount importance
cats. Our initial dose of oral DDAVP is 0.05 mg for dogs because relatively short periods of water restriction can have
weighing less than 5 kg and for cats, 0.1 mg for dogs weigh- catastrophic results (i.e., the development of hypernatremic,
ing 5 to 20 kg, and 0.2 mg for dogs weighing more than hypertonic dehydration, and neurologic signs).
20 kg given every 12 hours. The frequency of administration
is increased to every 8 hours if unacceptable PU and PD Prognosis
persist 1 week after therapy is initiated. Treatment should be Dogs and cats with idiopathic or congenital CDI usually
switched to the intranasal DDAVP preparation if minimal to become asymptomatic with appropriate therapy, and with
no response to oral DDAVP administered three times a day proper care these animals have an excellent life expectancy.
is noted. Decreasing the frequency of administration, Unfortunately, many owners discontinue DDAVP therapy or
decreasing the dose of DDAVP, or both can be tried once elect euthanasia of their pet after a few months because of
clinical response has been documented. Periodic monitoring the expense of DDAVP. Without therapy, these animals often
of serum electrolytes is also recommended and the dose of lead acceptable lives as long as water is constantly provided
DDAVP adjusted if hyponatremia develops. To date, most and they are housed in an environment that cannot be
dogs have required 0.1 to 0.2 mg of DDAVP two to three damaged by severe PU. However, the untreated animal is
times a day, and most cats have required 0.025 to 0.05 mg of always at risk for developing life-threatening dehydration if
DDAVP two to three times a day, for control of PU and PD. water is withdrawn for longer than a few hours. PU and PD
DDAVP parenteral (2 mL vials containing 4 µg/mL) can frequently resolve in dogs and cats with trauma-induced
be used in lieu of the nasal formulation or oral tablets. In CDI, often within 2 weeks of the traumatic incident. The
humans, parenteral administration of DDAVP is 5 to 20 prognosis in dogs and cats with hypothalamic and pituitary
times as potent as DDAVP nasal. The initial parenteral tumors is guarded to grave. Neurologic signs typically
dosage of DDAVP is 0.5 to 1.0 µg administered SC once a develop within 6 months after the diagnosis of CDI, and
day. Subsequent adjustments in the dose and frequency of clinical response to radiation therapy and chemotherapy is
administration are based on improvement in PU and PD, variable and unpredictable.
duration of clinical response, and changes in serum sodium The prognosis for animals with primary NDI is guarded
concentration. Hyponatremia is more apt to develop with to poor because of limited therapeutic options and a gener-
parenteral DDAVP than with tablets or nasal spray and can ally poor response to therapy. The prognosis for animals with
mimic the syndrome of inappropriate vasopressin secretion. secondary NDI depends on the prognosis of the primary
The maximal effect of DDAVP, regardless of the route of problem.
administration, occurs from 2 to 8 hours after administra-
tion, and the duration of action ranges from 8 to 24 hours.
Larger doses of DDAVP appear both to increase its antidi- PRIMARY (PSYCHOGENIC) POLYDIPSIA
uretic effects and to prolong its duration of action; however,
expense becomes a limiting factor. The medication may be Primary PD is defined as a marked increase in water intake
administered exclusively in the evening as insurance against that cannot be explained as a compensatory mechanism for
nocturia. excessive fluid loss. In humans, primary PD results from a
We have had excellent results in dogs and cats receiving defect in the thirst center or may be associated with mental
daily medication for longer than 5 years. Owners of dogs and illness. Primary dysfunction of the thirst center resulting in