Therapeutic Progress–review Xxviii: Platelet Function and Calcium Channel Blocking Agents

Platelets play a major role in the pathogenesis of vascular disorders such as coronary heart disease. The control of platelet function centres on the concentration of free intra-cellular Calcium ions (Ca2+). Increases in intracellular Ca2+ will result in platelet activation and release of substances such as thromboxane A2 which will stimulate further platelet activation and vasoconstriction, leading to vascular damage, thrombosis and ischaemia. Calcium channel blocking agents (CCB's) have the ability to reduce Ca2+ availability and may have potentially beneficial effects on platelet function. CCB's have been convincingly shown to have anti-platelet properties in vitro. They have also shown anti-platelet properties in vivo although this finding has not been consistent. In addition they have been shown to act synergistically with other anti-platelet agents. In the light of the available information it is likely that CCB's have only minor anti-platelet properties in vivo when used alone. Combining CCB's with other anti-platelet agents, however, may allow lower doses of drugs to be used to achieve a satisfactory inhibitory effect on platelet function. Such combination therapy may be of value in the treatment of vascular disorders; however, further studies are required to evaluate these effects in the clinical situation.