A variety of different pharmacologic agents have been reported to modulate whole blood viscosity. However, as Kelvin stated, our ability to understand is only as good as our ability to measure. The effect on human blood viscosity of warfarin, a widely used “blood thinner” medication, has not yet been studied. However, one prior animal study did report a viscosity-lowering effect [1].

Another therapeutic agent which has been considered to be a viscosity-lowering drug is pentoxifylline. However, this xanthine derivative indicated for claudication has actually demonstrated mixed results. Six different reports have shown reductions in viscosity with pentoxifylline [2-7], while at least five other peer-reviewed studies observed whole blood viscosity to be increased with pentoxifylline or no effect on blood viscosity [8-12].

Reductions in blood viscosity have not been observed with either ticlopidine [13] or cilostazol [14]. However, combination aspirin-dipyridamole was demonstrated in a controlled trial to lower blood viscosity significantly more than aspirin monotherapy [15].

  1. Amin TM, Sirs JA, Allen BV, Colles CM. Effects of warfarin on blood rheology in navicular disease. Res Vet Sci 1986; 40:308-12.
  2. Berman W Jr, Berman N, Pathak D, Wood SC. Effects of pentoxifylline (Trental) on blood flow, viscosity, and oxygen transport in young adults with inoperable cyanotic congenital heart disease. Pediatr Cardiol 1994; 15:66-70.
  3. Sonkin PL, Sinclair SH, Hatchell DL. The effect of pentoxifylline on retinal capillary blood flow velocity and whole blood viscosity. Am J Ophthalmol 1993; 115:775-80.
  4. Perego MA, Sergio G, Artale F, Giunti P, Danese C. Haemorrheological improvement by pentoxifylline in patients with peripheral arterial occlusive disease. Curr Med Res Opin 1986; 10:135-8.
  5. Solerte SB, et al. Retrospective analysis of long-term hemorheologic effects of pentoxifylline in diabetic patients with angiopathic complications. Acta Diabetol 1997; 34:67-74.
  6. Di Perri T, et al. Studies of the clinical pharmacology and therapeutic efficacy of pentoxifylline in peripheral obstructive arterial disease. Angiology 1984; 35:427-35.
  7. Ott E, Lechner H, Fazekas F. Hemorheological effects of pentoxifylline on disturbed flow behavior of blood in patients with cerebrovascular insufficiency. Eur Neurol 1983;22 Suppl 1:105-7.
  8. Dawson DL, et al. Failure of pentoxifylline or cilostazol to improve blood and plasma viscosity, fibrinogen, and erythrocyte deformability in claudication. Angiology 2002; 53:509-20.
  9. Brown MM. Effect of oxpentifylline on blood viscosity and cerebral blood flow in man. Br J Clin Pharmacol 1989; 28:488-92.
  10. Billett H, Kaul DK, Connel MM, Fabry ME, Nagel RL. Pentoxifylline (Trental) has no significant effect on laboratory parameters in sickle cell disease. Nouv Rev Fr Hematol 1989; 31:403-7.
  11. Reilly D, Quinton D, Barrie W. A controlled trial of pentoxifylline (Trental 400) in intermittent claudication: clinical, haemostatic and rheological effects. N Z Med J 1987; 100:445-7.
  12. Perhoniemi V. Effects of flunarizine and pentoxifylline on walking distance and blood rheology in claudication. Angiology 1984. 35:366-72.
  13. Fagher B, Persson S, Persson G, Larsson H. Blood viscosity during long-term treatment with ticlopidine in patients with intermittent claudication. A double-blind study. Angiology. 1993 4:300-6.
  14. Dawson DL, Zheng Q, Worthy SA, Charles B, Bradley DV Jr. Failure of pentoxyifylline or cilostazole to improve blood and plasma viscosity, fibrinogen and erythorcyte deforability in claudication. Angiology 2002; 53:509-20.
  15. Rosenson RS. Treatment with aspirin and dipyridamole is more effective than aspirin in reducing low shear blood viscosity. Microcirculation 2008; 15:615-20.