Dipyridamole Injection: Indications, Dosage, Precautions, Adverse Effects
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Dipyridamole Injection - Product Information

Manufacture: Fresenius Kabi USA, LLC
Country: Canada
Condition: Myocardial Infarction, Prophylaxis, Radionuclide Myocardial Perfusion Study
Class: Cardiac stressing agents, Platelet aggregation inhibitors, Vasodilators
Form: Liquid solution, Intravenous (IV)
Ingredients: Dipyridamole, polyethylene glycol, tartaric acid, hydrochloric acid, water for Injection

Actions and Clinical Pharmacology

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 (when administered intravenously for myocardial perfusion imaging) and ventricular function is also uncertain, but presumably represents a “steal” phenomenon. In this situation, relatively intact vessels dilate, and sustain enhanced flow, leaving reduced pressure and flow across areas of hemodynamically important coronary vascular constriction.

Following intravenous administration, the distribution half-life in man is about 25 minutes. When plasma levels of drug are followed for up to 60 hours after i.v., plasma levels decline tri - exponentially with half-lives of 5 minutes (i.v. only), 53 minutes and about 10 - 12 hours. The volume of distribution is about 140 litres with about 92 - 99% binding to plasma proteins, primarily alpha1-acid glycoprotein.

Indications and Clinical Uses

Myocardial Perfusion Imaging

Intravenous dipyridamole can be used to induce pharmacologic vasodilation for myocardial perfusion imaging.

Contraindications

Hypersensitivity to dipyridamole. Intravenous administration of dipyridamole is not recommended in states of shock or collapse.

Warnings

Rare serious adverse reactions associated with the administration of intravenous dipyridamole for myocardial imaging have been reported. These have included fatal and non-fatal myocardial infarction, ventricular fibrillation, symptomatic ventricular tachycardia, stroke and transient cerebral ischemia.

Since excessive doses of dipyridamole or intravenous doses given too rapidly can produce peripheral vasodilation, dipyridamole should be used with caution in patients with hypotension, rapidly worsening angina, subvalvular aortic stenosis or hemodynamic instability. In rare cases, such patients may be at risk for developing myocardial ischemia and infarction.

An intravenous bolus of dipyridamole (40 - 50 mg over 4 minutes) can result in chest pain in patients with coronary artery disease. Rarely, hypotension or ventricular arrhythmias occur with a rapid, i.v. bolus. The infusion rate should be monitored to minimize this risk. The symptoms can generally be reversed with an intravenous injection of 50 - 250 mg of aminophylline over several minutes.

Patients with a history or presence of bronchial hyperreactivity may be at risk of developing bronchospasm during the use of intravenous dipyridamole as an adjunct to myocardial perfusion imaging. Although the actual overall incidence of this occurrence is small (~ 0.2%), the clinical information to be gained through the use of intravenous dipyridamole should be weighed against the potential risk to the patient.

Precautions

Intravenous dipyridamole as an adjunct to myocardial perfusion imaging should be used with caution in patients with unstable angina, as such patients may be at risk for severe myocardial infarction.

As with exercise-induced stress, the use of intravenous dipyridamole as an adjunct to myocardial perfusion imaging may occasionally precipitate cardiac arrhythmias in patients with severe heart disease. Scanning should therefore be performed with constant monitoring of the patient's ECG. Parenteral aminophylline should be readily available and should be administered as a slow intravenous injection of 50 - 250 mg in the event of occurrences such as chest pain, bronchospasm, severe nausea/vomiting, hypotension, severe headache.

In the case of severe hypotension, the patient should be placed in a supine position with the head tilted down if necessary, before administration of parenteral aminophylline. If 250 mg of aminophylline does not relieve chest pain symptoms within a few minutes, sublingual nitroglycerin may be administered. If chest pain continues despite use of aminophylline and nitroglycerin, the possibility of myocardial infarction should be considered. If the clinical condition of a patient with an adverse event permits a one minute delay in the administration of parenteral aminophylline, thallium-201 may be injected and allowed to circulate for one minute before the injection of aminophylline. This will allow initial thallium perfusion imaging to be performed before reversal of the pharmacologic effects of dipyridamole on the coronary circulation.

Use in Pregnancy

Reproductive studies have been performed in mice, rats, and rabbits at doses of up to 125 mg/kg and have not revealed evidence of impaired embryonic development attributable to dipyridamole. However, there have not been adequate, well controlled studies in pregnant women and the drug should be used during pregnancy only if the expected benefits outweigh the potential risks.

Use in Lactation

Dipyridamole is excreted in human milk. Caution should therefore be used when this drug is administered to nursing mothers.

Use in Children

The safety and effectiveness of dipyridamole have not been established in the pediatric population.

Drug Interactions

The use of oral maintenance xanthines (e.g., theophylline, aminophylline) may abolish the coronary vasodilation produced by intravenous dipyridamole administration. This could lead to false negative imaging results. Xanthine derivatives (e.g., found in coffee, tea) may weaken the effect of dipyridamole.

Caution is necessary when dipyridamole is used concurrently with anticoagulants or thrombolytics as the combined use of such agents may result in an increased risk of hemorrhage.

Dipyridamole may increase the hypotensive effect of blood pressure lowering drugs.

Dipyridamole may counteract the anticholinesterase effect of cholinesterase inhibitors. In patients with myasthenia gravis, readjustment of therapy may be necessary during treatment with dipyridamole.

Adverse Reactions

Serious adverse events (fatal and non-fatal myocardial infarction, severe ventricular arrhythmias, and serious CNS abnormalities) associated with the intravenous administration of dipyridamole for myocardial imaging are described in WARNINGS.

When intravenous dipyridamole was used as an adjunct to myocardial perfusion imaging in a study of 3911 patients, the following events occurred in greater than 1% of the patients:

Event Description Incidence (%) of Occurrence in 3911 Patients
Chest pain/angina pectoris 19.7
Headache 12.2
Dizziness 11.8
Electrocardiographic Abnormalities/ST-T changes 7.5
Electrocardiographic Abnormalities/Extrasystoles 5.2
Hypotension 4.6
Nausea 4.6
Flushing 3.4
Electrocardiographic Abnormalities/Tachycardia 3.2
Dyspnea 2.6
Pain Unspecified 2.6
Blood Pressure Lability 1.6
Hypertension 1.5
Paresthesia 1.3
Fatigue 1.2

Less common events (i.e., occurred in 1% or less of the patients in the study) included, in decreasing order of frequency:

Cardiovascular System

Electrocardiographic abnormalities unspecified, arrhythmia unspecified, palpitation, ventricular tachycardia, bradycardia, myocardial infarction, AV block, syncope, orthostatic hypotension, atrial fibrillation, supraventricular tachycardia, ventricular arrhythmia unspecified, heart block unspecified, cardiomyopathy, edema.

Central and Peripheral Nervous System

Hypoesthesia, hypertonia, nervousness/anxiety, tremor, abnormal coordination, somnolence, dysphonia, migraine, vertigo.

Gastrointestinal System

Dyspepsia, dry mouth, abdominal pain, flatulence, vomiting, eructation, dysphagia, tenesmus, increased appetite.

Respiratory System

Pharyngitis, bronchospasm, hyperventilation, rhinitis, coughing, pleural pain.

Other

Myalgia, back pain, injection site reaction unspecified, diaphoresis, asthenia, malaise, arthralgia, injection site pain, rigor, earache, tinnitus, vision abnormalities unspecified, dysgeusia, thirst, depersonalization, eye pain, renal pain, perineal pain, breast pain, intermittent claudication, leg cramping.

Symptoms and Treatment of Overdosage

Hypotension, if it occurs, is likely to be of short duration but vasopressor substances may be used if necessary. Symptoms such as feeling warm, flushes, sweating, accelerated pulse, restlessness, feeling of weakness and dizziness, and anginal complaints may occur.

Dosage and Administration

Myocardial Perfusion Imaging

The dose of intravenous dipyridamole used as an adjunct to myocardial perfusion imaging should be adjusted according to the weight of the patient. Prior to use, Dipyridamole Injection, USP should be diluted 1:1 with Dextrose Injection, USP 5%. The diluted solution should be used within 6 hours after mixing. The recommended dose is 0.142 mg/kg/min., infused over 4 minutes. A total dose of greater than 60 mg is not recommended for use in any patient. The imaging agent should be injected within 5 minutes following the 4 minute infusion of dipyridamole. Do not mix i.v. dipyridamole with other drugs in the same syringe or infusion container.