Effects of calcium channel blockers on in vitro platelet function in whole blood using single platelet counting

The effects of various calcium channel blockers on in vitro platelet aggregation were studied using whole blood platelet counting. Diltiazem and verapamil inhibited aggregation caused by adrenaline 5 microM and collagen 2 micrograms/ml, but only at concentrations far in excess of those seen in clinical use. Nifedipine and nimodipine also inhibited aggregation to these agonists, but this seemed to be due to the solvent used. The solvent for these dihydropyridines contains 15% ethanol, 15% polyethylene glycol and 70% water, and the ethanol component is the most likely to have caused an antiaggregatory effect. Other studies showing an antiaggregatory effect of dihydropyridines may not have taken account of this solvent effect.