Initial treatment with desmopressin
Recommended initial doses of desmopressin vary depending on the route it is being administered. In most cats and smaller dogs, 1 to 2 drops of the intranasal preparation administered once or twice daily are sufficient to control polyuria and polydipsia (see Table below). Larger dogs may require up to 4 to 5 drops twice daily. Use of a tuberculin or insulin syringe allows for more accurate dosing. Application of desmopressin into the conjunctival sac may cause local irritation, as the solution is acidic. Some animals may object to the daily eye drops, making this route of administration ineffective.
With the subcutaneous route of administration, the initial recommended dose is 1.0 to 5.0 μg once or twice daily, depending on the size of the animals. If the nasal solution (100 µg /ml) were used for this purpose, one would inject only 0.01 to 0.05 ml (or 1 to 5 U with a U-100 insulin syringe). With the oral tablets, a starting dose of 0.05 mg to 0.2 mg (50 to 100 µg) once or twice daily is initiated.
Desmopressin dose adjustments
In dogs and cats with central diabetes insipidus, daily administration of desmopressin may completely eliminate polyuria and polydipsia. However, because of individual differences in absorption and metabolism, the dose required to achieve complete, around-the-clock control varies from patient to patient. The maximal effect of desmopressin occurs from 2 to 8 hours after administration, and the duration of action varies form 8 to 24 hours. Larger doses of the drug appear to both increase its antidiuretic effects and prolong its duration of action; however, expense can become a limiting factor for some owners.
No matter what route of administration is used, the daily dose should be gradually adjusted as needed to control signs of polydipsia and polyuria. The morning and evening doses can be adjusted separately if needed.
Adverse effects of desmopressin
Desmopressin is relatively safe for use in animals with central diabetes insipidus. Adverse effects of desmopressin are uncommon, but overdosage can lead to fluid retention, hyponatremia, and decreased plasma osmolality. Although extremely rare, fluid intoxication associated with desmopressin overdosage can lead to CNS disturbances including depression, increased salivation, vomiting, ataxia, muscle tremors, coma and convulsions. In such instances, furosemide can be given to induce diuresis.
To avoid the potential problem of overdosage, it is recommended that animals not be allowed free access to water immediately after each dose of desmopressin, especially if severe polydipsia and polyuria have redeveloped. Without such short-term (1 to 2 hours) water restriction, the cat many consume excessive amounts of water that cannot be subsequently excreted, as the desmopressin is absorbed and has its peak antidiuretic effects on the renal tubules.
Cost of desmopressin
The principle drawback with the use of any of the desmopressin preparations in the treatment of central diabetes insipidus is the drug’s considerable expense. The oral route of administration is the most expensive, while the subcutaneous route of administration (using the sterilized nasal solutions) is generally the most cost-effective.