Abstract 10210: Effects of Chronic Treatment With the Phosphodiesterase-5 Inhibitors Sildenafil and Tadalafil on Platelet Aggregation in Patients With Eisenmenger Syndrome

Abstract

Background: Patients with pulmonary arterial hypertension (PAH) associated with the Eisenmeger syndrome (ES) frequently have decreased platelet counts and aggregation. This is probably due to chronic endogenous platelet activation and consumption associated with hypoxemia and blood hyperviscosity, with "exhausted" platelets present in circulation. When platelets are analyzed in vitro, decreased response to aggregation inducing agents is generally observed. Purpose: Since phosphodiesterase-5 inhibitors (PDE-5Is) are frequently used in the management of PAH, we investigated, the effects of sildenafil and tadalafil on in vitro platelet aggregation (PA) in adults with ES. Methods: Twenty-three naïve patients aged 28 (22-47) years (median and interquartile range) were randomly assigned to oral treatment with sildenafil (20mg t.i.d., N=11) or tadalafil (single daily dose of 40mg, N=12). Baseline spO 2 , Ht, Hb level and platelet count were 87% (80-92%), 52% (49-60%), 17 (16-20)g/dL and 205 (158-248) x 10 3 pl/μL, respectively. Data were collected at baseline, 90 and 180 days of treatment. Whole blood PA was analyzed by the impedance method. Results are expressed as percent normal. Results: Treatment with PDE-5Is resulted in decrease Ht and Hb level (p<0.001), but no change in platelet count. When patients analyzed as a whole (N=23), ADP-induced PA was 44% (23-91%), 54% (23-87%) and 71% (42-124%) respectively at baseline, 90 and 180 days (p=0.029). Collagen-induced PA was 55% (23-138%), 96% (67-162%) and 146% (62-187%), respectively (p=0.041). When treatment groups were investigated separately at 180 days, collagen-induced PA was 2.7 (1.1-11.1) times baseline in sildenafil-treated patients, and 1.8 (0.6-4.2) times baseline in the tadalafil group. ADP-induced PA was 2.2 (1.3-4.8) times baseline in the sildenafil , but 1.0 (0.7-3.6) time baseline for tadalafil. Conclusion: In ES patients, PDE-5Is therapy is associated with improvement of PA. This may be due to decelerated endogenous platelet activation associated with hemodynamic improvement. However, particularly for sildenafil, some patients may become transiently at a higher risk of thrombotic events, as PA increases far above normal levels.