Do calcium antagonists affect platelets?

Inappropriate platelet activation is thought to have a pathophysiological role in several cardiovascular disorders, including ischaemic heart disease and hypertension. Calcium antagonists are increasingly used in the therapy of these diseases. An inhibitory effect on platelet activation would clearly be a useful component of their therapeutic effect. Since a raised intracellular calcium concentration is crucial for platelet activation, and much of the calcium enters from the extracellular medium, such an effect might be anticipated. In fact, calcium antagonists consistently inhibit platelet activation in vitro, and somewhat less consistently ex vivo. However, many unanswered questions remain. Clinically attained drug concentrations in plasma may be too low to be effective, there appear to be no calcium antagonist receptors on the platelet, and the mechanism of action of the drugs is unclear. More importantly, it is not known whether an anti-platelet effect, if it occurs, is of practical rather than theoretical, value to the patient. These problems will need much more investigation.