Dipyridamole

Dipyridamole Injection is indicated as an alternative to exercise in thallium myocardial perfusion imaging for the evaluation of coronary artery disease in patients who cannot exercise adequately. In a study of about 1100 patients who underwent coronary arteriography and Dipyridamole Injection assisted thallium imaging, the results of both tests were interpreted blindly and the sensitivity and specificity of the dipyridamole thallium study in predicting the angiographic outcome were calculated. The sensitivity of the dipyridamole test (true positive dipyridamole divided by the total number of patients with positive angiography) was about 85%. The specificity (true negative divided by the number of patients with negative angiograms) was about 50%.

Dipyridamole is a coronary vasodilator in man. The mechanism of vasodilation has not been fully elucidated, but may result from inhibition of uptake of adenosine, an important mediator of coronary vasodilation. The vasodilatory effects of dipyridamole are abolished by administration of the adenosine receptor antagonist theophylline. How dipyridamole-induced vasodilation leads to abnormalities in thallium distribution and ventricular function is also uncertain but presumably represents a “steal” phenomenon in which relatively intact vessels dilate and sustain enhanced flow, leaving reduced pressure and flow across areas of hemodynamically important coronary vascular constriction.

The dose of intravenous Dipyridamole Injection as an adjunct to thallium myocardial perfusion imaging should be adjusted according to the weight of the patient. The recommended dose is 0.142 mg/kg/min (0.57 mg/kg total) infused over 4 minutes. Although the maximum tolerated dose has not been determined, clinical experience suggests that a total dose beyond 60 mg is not needed for any patient. Prior to intravenous administration, Dipyridamole Injection should be diluted in at least a 1:2 ratio with sodium chloride injection 0.45%, sodium chloride injection 0.9% or dextrose injection 5% for a total volume of approximately 20 to 50 mL. Infusion of undiluted dipyridamole may cause local irritation. Thallium-201 should be injected within 5 minutes following the 4-minute infusion of dipyridamole. Do not mix Dipyridamole Injection with other drugs in the same syringe or infusion container.

Hypersensitivity to dipyridamole or any of the other components of the drug.

Serious adverse reactions associated with the administration of intravenous Dipyridamole Injection have included cardiac death, fatal and non-fatal myocardial infarction, ventricular fibrillation, symptomatic ventricular tachycardia, stroke, transient cerebral ischemia, seizures, anaphylactoid reaction, bronchospasm, severe hypotension, anaphylaxis with laryngospasm, and angioedema. There have been reported cases of asystole, sinus node arrest, sinus node depression and conduction block. Patients with abnormalities of cardiac impulse formation/conduction or severe coronary artery disease may be at increased risk for these events.

Adverse reaction information concerning intravenous Dipyridamole Injection is derived from a study of 3911 patients in which intravenous dipyridamole was used as an adjunct to thallium myocardial perfusion imaging and from spontaneous reports of adverse reactions and the published literature. Serious adverse events (cardiac death, fatal and non-fatal myocardial infarction, ventricular fibrillation, asystole, sinus node arrest, symptomatic ventricular tachycardia, stroke, transient cerebral ischemia, seizures, anaphylactoid reaction, angioedema, and bronchospasm) are described above. In a study of 3911 patients, the most frequent adverse reactions were: chest pain/angina pectoris (19.7%), electrocardiographic changes (most commonly ST-T changes) (15.9%), headache (12.2%) and dizziness (11.8%).

Oral maintenance theophylline and other xanthine derivatives such as caffeine may abolish the coronary vasodilatation induced by intravenous Dipyridamole Injection administration. This could lead to a false negative thallium imaging result. Myasthenia gravis patients receiving therapy with cholinesterase inhibitors may experience worsening of their disease in the presence of dipyridamole.

Store at 25ºC (77ºF), excursions permitted between 15º to 30ºC (59º to 86ºF). Avoid freezing. Storage PROTECT FROM LIGHT: Keep covered in carton until time of use.