### Description

A patient with von Willebrand Disease (vWD) may respond to a test dose of desmopressin with increased plasma levels of Factor VIII and von Willebrand's factor (vWF).

Test dose of desmopressin: 0.3 micrograms per kg in 50 mL normal saline infused intravenously over 30 minutes.

The time to the maximum plasma concentration of Factor VIII and von Willebrand factor is about 1 hour.

Assuming a first order elimination:

concentration at time t in IU/mL=

= (maximum concentration in IU/mL) * EXP((-1) * (elimination rate constant) * (hours since peak reached))

where:

• The assumption is that the plasma concentrations of Factor VIII and vWF are low.

• If the plasma levels are higher, then the elimination equation needs to be adjusted for the baseline concentration, with increase from desmopressin = (measured value) - (baseline value).

If the concentration is measured at t hours (often about 4 hours later):

elimination rate constant =

= LN((maximum concentration) / (concentration at time t)) / (time in hours)

half life in hours =

= 0.693 / (elimination rate constant)

Interpretation:

• The half-life is normally 5 to 8 hours.

• Peak levels of 0.4 to 0.6 IU/mL for both Factor VIII and vWF is sufficient for minor surgery.

• Peak levels of > 1.0 IU/mL may be needed for major surgery.

• The response of Factor VIII and von Willebrand factor differs depending on the type of von Willebrand's disease that the patient has.

 Type of vWD Factor VIII Response vWF Response Type 1 very high peak but short half-life very high peak but short half-life Type 2N poor normal Type 2A normal poor