Antiplatelet Therapies

Antiplatelet medications are widely used to prevent thrombus formation and acute cardiovascular disease events. Two clinical studies examined the effect of aspirin on blood viscosity and suggested that aspirin may have a viscosity-lowering effect [1, 2]. However, the most authoritative study on the effect of aspirin on blood viscosity was a randomized, double-blind, placebo-controlled study of 100 healthy, nonsmoking, adult males with normal lipid levels, using an automated scanning capillary viscometer. The study showed that aspirin had no significant effect on blood viscosity [3].

Using the same automated scanning capillary viscometer, aspirin plus dipyridamole was shown to be more effective than aspirin alone in reducing whole blood viscosity at low-shear rates in patients with high homocysteine levels and stable cardiovascular disease [4]. This dipyridamole study was performed as a follow-up to the European/Australasian Stroke Prevention in Reversible Ischemia Trial (ESPRIT), a multi-center randomized controlled trial which showed that combination therapy of aspirin/dipyridamole reduced cardiovascular disease events and death after stroke as compared with aspirin alone [5].

Clopidogrel was demonstrated to reduce low-shear blood viscosity levels by 18% from baseline levels three weeks after administration [6]. High-shear blood viscosity levels were also reduced by a mean of 10% from baseline after the third week (p values < 0.01). These findings were based on a double-blind, placebo-controlled study of 30 age- and gender-matched individuals with impaired blood viscosity and evidence of carotid and/or femoral atherosclerosis.

  1. Bozzo J, Hernandez MR, Ordinas A. Reduced red cell deformability associated with blood flow and platelet activation: improved by dipyridamole alone or combined with aspirin. Cardiovasc Res 1995; 30:725-30.
  2. Bozzo J, Escolar G, Hernandez MR, Galán AM, Ordinas A. Prohemorrhagic potential of dipyrone, ibuprofen, ketorolac, and aspirin: mechanisms associated with blood flow and erythrocyte deformability. J Cardiovasc Pharmacol 2001; 38:183-190.
  3. Rosenson RS, Wolff D, Green D, Boss AH, Kensey KR. Aspirin. Aspirin does not alter native blood viscosity. J Thromb Haemost 2004; 2:340-1.
  4. Rosenson RS. Treatment with aspirin and dipyridamole is more effective than aspirin in reducing low shear blood viscosity. Microcirculation 2008; 15:615-20.
  5. ESPRIT Study Group, Halkes PH, van Gijn J, Kappelle LJ, Koudstaal PJ, Algra A. Aspirin plus dipyridamole versus aspirin alone after cerebral ischaemia of arterial origin (ESPRIT): randomised controlled trial. Lancet 2006; 367:1665-73.
  6. Ciuffetti G, Lombardini R, Pirro M, Lupattelli G, Mannarino E. Clopidogrel: hemorheological effects in subjects with subclinical atherosclerosis. Clin Hemorheol Microcirc 2001; 25:31-9.