Introduction. Despite the fact that desmopressin (DDAVP) is considered the treatment of choice in the majority of patients with inherited von Willebrand disease (VWD), there are still open questions about the efficacy and safety of the use of DDAVP to manage recurrent bleeding episodes, delivery and major surgery. In fact, to avoid tachyphylaxis and possible side effects with repeated DDAVP injections, VWF concentrates are usually preferred to manage delivery and major surgery also in VWD patients proven to be DDAVP-responsive. No prospective data have been reported so far to correlate biological response with DDAVP clinical efficacy in VWD and guide clinical practice.Design, aims and methods. ProDesWilis an investigator-driven Pro spective study on D esmopressin e fficacy and s afety of patients with inherited von Wil lebrand disease assessed at enrolment for DDAVP biological response during a test-infusion. Inclusion criteria: VWD diagnosis without any age restriction according to bleeding score >4, VWF activity levels <45U/dL, and at least another affected member in the family. DDAVP Biological Response: VWD were classified as complete, partial or no-responders as previously reported (Blood 2008;111:3531). Treatment regimens: DDAVP given intravenously or subcutaneously (0.3 ug/Kg) or by nasal spray (4 ug/Kg) according to preparations available in different countries with or without standard doses of anti-fibrinolytic agents (Epsilon-amino-caproic acid, EACA or tranexamic acid, TA). In case of major surgery, DDAVP was used together with TA using a 3dayOn-4dayOff-3dayOn schedule. DDAVP efficacy-safety evaluated with criteria currently used for VWF concentrates, with poor efficacy defined when VWF concentrates were needed. Patients were prospectively followed up for 24 months by ProDesWil Investigators who reported detailed information about DDAVP therapy used for bleeds, deliveries, oral and minor/major surgeriesResults. 268 patients were enrolled in this 24-month prospective study. DDAVP-biological response: 225/268 (85%) patients met inclusion criteria as VWD1(n=184), VWD1C (n=14), VWD2A(n=15), VWD2M(n=12). The 14 VWD1C with accelerated clearance carried C1130F and R1205H mutations. DDAVP biological response was complete, partial and absent in 89%, 10% and 1% of all VWD. DDAVP clinical efficacy and safety: during the 24-month follow-up 84/225 (37.3%) received DDAVP for bleeding episodes (n=104), oral surgeries (n=33), deliveries (n=12), other minor/major surgeries (n=25). Total DDAVP injections were 652 with median, range/episode during bleeds (2,1-12), oral surgeries (1,1-10), deliveries (3,1-13), minor/major surgeries (3.6,1-16). Clinical efficacy was excellent/good in bleeds (93.3%), oral surgery (100%), deliveries (91.7%), minor/major surgeries (92.3%). All VWD treated for oral surgery with (75%) and without (25%) EACA/TA had excelled/good outcomes. Efficacy was rated excellent/good in 96/104 bleeds, with 8 episodes rated poor during menorrhagia (n=4) in 2 VWD1 and 2 VWD2A, during nose (n=2) and gastrointestinal (n=2) bleeds in 3 VWD2A and 1 VWD1C. 11/12 deliveries had excellent/good outcome with poor response in only one VWD1C who required VWF concentrates after caesarean section. All the 11/25 cases with minor surgeries had excellent outcomes. Among the 14/25 major surgeries [abdominal (n=5), hysterectomy (n=3), tonsillectomy (n=3), orthopaedic and others (n=3)] 2 episodes (partial resection of kidney in VWD2A and tonsillectomy in VWD1) were rated poor. Side effects (16 cases) were mainly minor (flushing, headache, tachycardia) with water retention reported only in 2 patients who received >12 doses of DDAVP for delivery or major surgery.Conclusions: DDAVP is an effective, safe and cheap treatment for managing patients with mild-moderate VWD who showed complete biological response to this drug. Therefore, DDAVP must be always recommended as first line therapy in responsive VWD not only in bleeds and oral surgery but also in deliveries and major surgeries. On the other hands, DDAVP should be used with caution in VWD2A and VWD1 with partial response. The additional use of EACA/TA should be considered especially when DDAVP is required for more than 4 days. DisclosuresNo relevant conflicts of interest to declare.