Dipyridamole

Common indications

• Cerebrovascular disease for secondary prevention of stroke. Dipyridamole is currently first-line therapy following a transient ischaemic attack, and second-line therapy following an ischaemic stroke where clopidogrel is contraindicated or not tolerated. It should usually be given in combination with aspirin but can be used as monotherapy if aspirin is contraindicated or not tolerated.
• To induce tachycardia during a myocardial perfusion scan in the diagnosis of ischaemic heart disease.

 

Mechanisms of action

• Dipyridamole has both antiplatelet and vasodilatory effects. 
• Although the exact mechanism of its antiplatelet action is controversial, the end effect is an increase in intra-platelet cyclic adenosine monophosphate (cAMP) that inhibits platelet aggregation, reducing the risk of arterial occlusion. 
• Dipyridamole also blocks cellular uptake of adenosine, prolonging its effect on blood vessels to produce vasodilation.

 

Important adverse effects

• The side effects of dipyridamole relate to its vasodilatory effects and include headache, flushing, dizziness and gastrointestinal symptoms that normally improve with time. 
• As with other antiplatelet agents there is an increased risk of bleeding. 
• Rarely dipyridamole can affect platelet numbers as well as function, causing thrombocytopaenia.

 

Warnings

• Dipyridamole should be used with caution in patients with ischaemic heart disease, aortic stenosis and heart failure as it causes vasodilatation and tachycardia that can exacerbate these conditions. 
• This effect is exploited diagnostically in myocardial perfusion scans, where radionucleotide distribution is compared in heart muscle at baseline and during tachycardia induced by intravenous dipyridamole. 
• Reduced perfusion after dipyridamole indicates cardiac ischaemia. 

 

Important interactions

• Dipyridamole inhibits cellular uptake of adenosine. 
• This prolongs its effects on the heart, increasing the risk of cardiac arrest. The dose of adenosine should therefore be reduced in patients treated with dipyridamole. 
• There is an increased risk of bleeding where dipyridamole is combined with other antiplatelet agents (aspirin, clopidogrel) and anticoagulants (heparin, warfarin).