dipyridamole
Persantine

Available forms
Available by prescription only
Injection: 10 mg/2 ml
Tablets: 25 mg, 50 mg, 75 mg

Indications and dosages
 Alternative to exercise in thallium myocardial perfusion imaging. Adults: 0.142 mg/kg/ minute I.V. infused over 4 minutes (0.57 mg/kg total).
 Inhibition of platelet adhesion in patients with prosthetic heart valves, in combination with warfarin or aspirin. Adults: 75 to 100 mg P.O. q.i.d.
 Prevention of thromboembolic complications in patients with various thromboembolic disorders other than prosthetic heart valves ◇. Adults: 150 to 400 mg P.O. daily (with warfarin or aspirin).

Pharmacodynamics
Coronary vasodilating action: Dipyridamole increases coronary blood flow by selectively dilating the coronary arteries. Coronary vasodilator effect follows inhibition of serum adenosine deaminase, which allows accumulation of adenosine, a potent vasodilator.
Platelet aggregation inhibitor action: Dipyridamole inhibits platelet adhesion by inhibition of red blood cell uptake of adenosine (an inhibitor of platelet reactivity), phosphodiesterase inhibition, and inhibition of thromboxane A₂ (a platelet activator).

Pharmacokinetics
Absorption: Absorption is variable and slow; bioavailability ranges from 27% to 59%.
Distribution: Wide distribution into body tissues; small amounts cross the placental barrier. Protein-binding ranges from 91% to 97%.
Metabolism: Metabolized by the liver.
Excretion: Elimination occurs via biliary excretion of glucuronide conjugates. Some dipyridamole and conjugates may undergo enterohepatic circulation and fecal excretion; a small amount is excreted in urine. Half-life varies from 1 to 12 hours.

Contraindications and precautions
No known contraindications. Use cautiously in patients with hypotension.

Interactions
Drug-drug. Adenosine: May increase plasma levels and CV effects of adenosine. Adenosine dosage may need adjustment.
Aminophylline: Inhibits dipyridamole action. Avoid use together.
Cholinesterase inhibitors: May counteract effects of cholinesterase inhibitors. Avoid use together.
Heparin, oral anticoagulants: Enhances anticoagulant effects. Monitor patient closely.

Adverse reactions
CNS: headache, dizziness.
CV: flushing, fainting, hypotension; angina, chest pain, blood pressure lability, hypertension (with I.V. infusion).
GI: nausea, vomiting, diarrhea, abdominal distress.
Hematologic: increased bleeding time.
Skin: rash, irritation (with undiluted injection), pruritus.

Effects on lab test results
None reported.

Overdose and treatment
Effects of overdose include peripheral vasodilation and hypotension.
 Maintain blood pressure and treat symptomatically.

Special considerations
• Give drug at least 1 hour before meals.
• When used as a pharmacologic stress test, total doses beyond 60 mg appear to be unnecessary.
• Dilute I.V. form to at least a 1:2 ratio with 0.45% saline injection, normal saline injection, or D₅W to a total volume of 20 to 50 ml. Inject thallium within 5 minutes of dipyridamole.
Breast-feeding patients
• Safety in breast-feeding women hasn’t been established.
Pediatric patients
• Dosage in children hasn’t been established.

Patient education
• Explain that clinical response may require 2 to 3 months of continuous therapy; encourage patient compliance.
• Discuss adverse reactions and how to manage therapy.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use