Usage
Dipyridamole is primarily prescribed as an antiplatelet agent to inhibit blood clot formation. It’s specifically indicated for:
- Prevention of stroke: As an adjunct to aspirin for secondary prevention of ischemic stroke and transient ischemic attacks.
- Prevention of thromboembolism: Post-cardiac valve replacement, used in conjunction with warfarin.
- Myocardial perfusion imaging: Used as a vasodilator during thallium myocardial perfusion imaging in patients unable to exercise adequately.
Dipyridamole’s pharmacological classification is antiplatelet agent.
It inhibits platelet aggregation, though the exact mechanism isn’t fully understood. It is thought to involve several pathways, including:
- Increasing adenosine levels
- Inhibiting phosphodiesterase
- Blocking platelet uptake of adenosine
Alternate Names
How It Works
Pharmacodynamics: Dipyridamole is a coronary vasodilator that increases coronary blood flow by dilating small resistance vessels supplying the heart. Its primary mechanism of action involves inhibiting platelet aggregation. This is mainly due to blocking adenosine uptake by platelets and other cells, as well as inhibiting phosphodiesterase, resulting in increased adenosine levels and vasodilation.
Pharmacokinetics:
- Absorption: Well-absorbed orally.
- Metabolism: Extensively metabolized in the liver, primarily via conjugation with glucuronic acid.
- Elimination: Excreted mainly in the bile and feces, with minimal renal excretion.
Mode of Action: At the cellular level, dipyridamole increases intracellular cyclic AMP (cAMP) and cyclic GMP (cGMP) by inhibiting phosphodiesterase enzymes. It also blocks cellular uptake of adenosine, increasing extracellular adenosine concentrations. These mechanisms decrease platelet adhesiveness and prevent aggregation.
Elimination pathways: Primarily hepatic metabolism and biliary excretion.
Dosage
Standard Dosage
Adults:
- Oral (Extended-release capsules): 200 mg twice daily.
- Oral (Tablets): 75-100 mg four times daily as an adjunct to warfarin for thromboembolism prophylaxis post-cardiac valve replacement.
- Intravenous (Myocardial perfusion imaging): 0.142 mg/kg/min infusion over 4 minutes (maximum 70 mg).
Children:
Limited data available. Not generally recommended for children under 12 years old. If used, 2-6 mg/kg/day divided every 6-8 hours may be considered.
Special Cases:
- Elderly Patients: No dose adjustment necessary, but use with caution in patients with hypotension, severe coronary artery disease, or hemodynamic instability.
- Patients with Renal Impairment: No dose adjustment necessary.
- Patients with Hepatic Dysfunction: Use with caution; no established dose adjustment, but may require lower initial doses.
- Patients with Comorbid Conditions: Use with caution in patients with hypotension, severe coronary artery disease, unstable angina, recent myocardial infarction, or myasthenia gravis.
Clinical Use Cases
Dipyridamole is not typically used in clinical scenarios like intubation, surgical procedures, mechanical ventilation, ICU use, or emergency situations like cardiac arrest.
Dosage Adjustments
No specific dose modifications based solely on renal/hepatic dysfunction are recommended. However, clinical judgment should guide dose adjustments based on individual patient conditions and comorbidities.
Side Effects
Common Side Effects
- Headache
- Dizziness
- Stomach upset
- Diarrhea
- Flushing
Rare but Serious Side Effects
- Severe allergic reactions (difficulty breathing, hives, swelling)
- Chest pain
- Myocardial ischemia
- Fainting
- Unusual bleeding or bruising
Long-Term Effects
No specific long-term effects have been reported.
Adverse Drug Reactions (ADR)
Severe allergic reactions and myocardial ischemia warrant immediate medical intervention.
Contraindications
- Hypersensitivity to dipyridamole
- Severe coronary artery disease (including unstable angina)
- Hemodynamic instability
- Active wheezing or bronchospastic lung disease
Drug Interactions
Dipyridamole interacts with several medications, including:
- Adenosine: Enhanced cardiovascular effects of adenosine.
- Anticoagulants (e.g., warfarin): Increased risk of bleeding.
- Antiplatelet agents: Increased risk of bleeding.
- Theophylline: May reduce dipyridamole’s effectiveness.
- Abrocitinib, riociguat: Contraindicated due to severe drug interactions.
Consult a comprehensive drug interaction resource before co-administering dipyridamole with other medications.
Pregnancy and Breastfeeding
- Pregnancy: Limited safety data; use only if the potential benefits outweigh the potential risks.
- Breastfeeding: Small amounts are excreted in breast milk; use cautiously and monitor the infant for bruising or bleeding.
Drug Profile Summary
- Mechanism of Action: Antiplatelet agent; inhibits platelet aggregation, possibly by increasing adenosine levels and inhibiting phosphodiesterase.
- Side Effects: Headache, dizziness, stomach upset, diarrhea, flushing; rarely severe allergic reactions, chest pain, myocardial ischemia.
- Contraindications: Hypersensitivity to dipyridamole, severe coronary artery disease, hemodynamic instability.
- Drug Interactions: Adenosine, anticoagulants, antiplatelet agents, theophylline, abrocitinib, riociguat.
- Pregnancy & Breastfeeding: Limited safety data; use with caution.
- Dosage: Varies by indication and formulation; consult dosing guidelines above.
- Monitoring Parameters: Monitor for signs of bleeding, chest pain, and allergic reactions.
Popular Combinations
- Aspirin: Commonly combined with aspirin for secondary prevention of ischemic stroke.
Precautions
- General Precautions: Assess for cardiovascular disease, hypotension, and coagulation disorders.
- Specific Populations: Use with caution in pregnancy, breastfeeding, and patients with hepatic impairment.
- Lifestyle Considerations: Alcohol may enhance dipyridamole’s hypotensive effects.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Dipyridamole?
A: Depends on the indication and formulation (see dosage section).
Q2: How does dipyridamole work to prevent strokes?
A: Primarily by inhibiting platelet aggregation, preventing blood clot formation in blood vessels leading to the brain.
Q3: What are the common side effects of dipyridamole?
A: Headache, dizziness, stomach upset, diarrhea, and flushing.
Q4: Is dipyridamole safe during pregnancy?
A: Limited safety data; use only if potential benefits outweigh potential risks.
Q5: Can dipyridamole be used in children?
A: Limited data available; generally not recommended for children under 12 years old. If used, dose adjustments are necessary based on weight.
Q6: How should dipyridamole be administered for myocardial perfusion imaging?
A: Intravenously at a dose of 0.142 mg/kg/min infused over 4 minutes (maximum 70 mg).
Q7: What are the key drug interactions to be aware of with dipyridamole?
A: Anticoagulants, antiplatelet agents, adenosine, theophylline, abrocitinib, and riociguat.
Q8: What are the contraindications to using dipyridamole?
A: Hypersensitivity, severe coronary artery disease, hemodynamic instability, active wheezing, or bronchospastic lung disease.
Q9: What precautions should be taken when prescribing dipyridamole to elderly patients?
A: Use with caution in those with hypotension, severe coronary artery disease, or hemodynamic instability.
Q10: Can dipyridamole be used in patients with renal impairment?
A: Yes, no dosage adjustment is typically necessary.
