What's the Best Dosage of Desmopressin when Injected Subcutaneously?

In a recent blog, you mentioned using compounded desmopressin (0.01%) that could be injected subcutaneously (SC).  I have 3 questions about the use of this desmopressin preparation:

1. What dose do you recommend for this formulation (per patient or per kg)? 
2. I've read elsewhere that the dose should be 2 µg per patient, administered once or twice daily. Would you agree with this (i.e., dosing independent of the weight of the patient)? 
3. I believe 0.01% is 100 µg/ml, correct?  If I use a U-100 insulin syringe, would this mean 2 units of the compounded formulation per dose? 

My Response:

Dose of desmopressin for SC injection
The empirical starting dose that I use for injectable desmopressin administered subcutaneously is 1–5 μg once or twice daily, depending on the size of the dog and response to therapy (1,2). As might be expected, larger-breed dogs tend to need more drug to control polyuria and polydipsia, and these bigger dogs will tolerate higher doses.

To make dosing easier, I usually have the owners draw up and administer the desmopressin with a U-100 low-dose insulin syringe. You are correct in that 0.01% is 100 µg/ml, so injecting 1-5 µg would be 1-5 units in this syringe.

Water intoxication is possible with use of this drug, so I do recommend monitoring of serum sodium concentrations, especially when high doses are given (1,3,4).

Formulations of desmopressin that can be injected
An injectable sterile solution of desmopressin acetate (4 µg/ml) marketed for intravenous use is available commercially and can be used in animals with diabetes insipidus (2). However, the cost of the injectable desmopressin is approximately 7 to 15 times higher per µg than the intranasal preparation, making this formulation cost-prohibitive for use in most dogs and cats.

The human nasal preparation of desmopressin can also be administered subcutaneously, but that preparation is not sterile and not authorized for this route (1,2).

Therefore, I generally use a compounded, veterinary, injectable formulation, which has already been sterilized by the compounding pharmacy and is safe to inject subcutaneously. This form is much cheaper than the injectable solution of desmopressin marketed for parenteral use in human patients.

References:

1. Shiel RE. Disorders of vasopressin production. In: Mooney CT, Peterson ME, eds. BSAVA Manual of Canine and Feline Endocrinology, Fourth ed. Gloucester: British Small Animal Veterinary Association; 2012:1-13. 
2. Peterson ME. What Drugs Do We Use to Treat Diabetes Insipidus? Insights in to Veterinary Endocrinology blog post, January 13, 2011. 
3. Robson WL. Water intoxication in patients treated with desmopressin. Pharmacotherapy 1996;16:969-970.
4. Bernstein SA, Williford SL. Intranasal desmopressin-associated hyponatremia: a case report and literature review. J Fam Pract 1997;44:203-208.