ASPIRIN AND DIPYRIDAMOLE
Clinical safety rating: safe
Theophylline may antagonize the antiplatelet effect Can cause angina pectoris and hypotension in patients with coronary artery disease.
Aspirin irreversibly inhibits cyclooxygenase-1 and -2 (COX-1/COX-2), reducing thromboxane A2 synthesis and platelet aggregation. Dipyridamole inhibits phosphodiesterase and blocks adenosine uptake, increasing intracellular cAMP and potentiating prostacyclin effects, leading to vasodilation and antiplatelet activity.
| Metabolism | Aspirin is hydrolyzed to salicylate; salicylate is conjugated with glycine (salicyluric acid) and glucuronic acid, and oxidized to gentisic acid. Dipyridamole is metabolized by the liver via conjugation with glucuronic acid. |
| Excretion | Aspirin: renal excretion of salicylate and metabolites (75% as salicyluric acid, 10% as salicyl phenolic glucuronide, 10% as salicyl acyl glucuronide, 5% as gentisic acid); Dipyridamole: primarily biliary excretion (80% as glucuronide conjugate), with enterohepatic circulation; renal excretion of unchanged drug is <5%. |
| Half-life | Aspirin: 15-20 minutes (low doses), 2-3 hours (anti-inflammatory doses); Dipyridamole: biphasic with terminal half-life of 10-12 hours (single dose) and 20-30 hours (chronic dosing due to enterohepatic recirculation). |
| Protein binding | Aspirin: 80-90% bound to albumin (saturable); Dipyridamole: 91-99% bound to alpha1-acid glycoprotein and albumin. |
| Volume of Distribution | Aspirin: 0.15-0.2 L/kg (low, reflects high protein binding); Dipyridamole: 1-3 L/kg (large, extensive tissue distribution, especially liver). |
| Bioavailability | Aspirin: 50-75% oral (first-pass hydrolysis to salicylate); Dipyridamole: 30-60% oral (conventional), 66-76% oral (extended-release); IV bioavailability 100%. |
| Onset of Action | Aspirin: 5-30 minutes oral (antiplatelet); Dipyridamole: 15-30 minutes oral (vasodilation), 0.5-1 hour oral for antiplatelet effect; IV: immediate for vasodilation. |
| Duration of Action | Aspirin: antiplatelet effect lasts for lifetime of platelet (7-10 days); Dipyridamole: antiplatelet effect lasts 24 hours (conventional), 12 hours (extended-release); vasodilation lasts 1-2 hours (IV). |
One capsule (aspirin 25 mg/dipyridamole 200 mg) orally twice daily.
| Dosage form | CAPSULE, EXTENDED RELEASE |
| Renal impairment | GFR 30-59 mL/min: No adjustment. GFR <30 mL/min: Avoid use due to risk of accumulation. |
| Liver impairment | Child-Pugh Class A: No adjustment. Child-Pugh Class B or C: Contraindicated due to increased bleeding risk. |
| Pediatric use | Safety and efficacy not established; use not recommended. |
| Geriatric use | No specific dose adjustment required; monitor for bleeding and renal function. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Theophylline may antagonize the antiplatelet effect Can cause angina pectoris and hypotension in patients with coronary artery disease.
| FDA category | Animal |
| Breastfeeding | Both aspirin and dipyridamole are excreted into breast milk. M/P ratio for aspirin: approximately 0.03-0.09; for dipyridamole: not well established but likely low. Risk of Reye syndrome in infants with aspirin; dipyridamole is generally considered compatible. Caution is advised, especially with high doses or long-term use. |
| Teratogenic Risk |
■ FDA Black Box Warning
No FDA black box warning.
| Common Effects | Headache |
| Serious Effects |
["Hypersensitivity to aspirin, dipyridamole, or any component of the formulation","Children and adolescents with viral infections (due to aspirin component and Reye's syndrome risk)","Active peptic ulcer disease or GI bleeding","Severe hepatic impairment","Severe renal impairment (CrCl < 10 mL/min)","Bleeding disorders (e.g., hemophilia)","Third trimester of pregnancy (aspirin-related risk of premature ductus arteriosus closure)"]
| Precautions | ["Risk of bleeding (e.g., may cause increased bleeding during surgery, avoid use in patients with active bleeding)","Hypersensitivity reactions (e.g., bronchospasm, angioedema, especially in patients with asthma or NSAID sensitivity)","Reye's syndrome risk in children with viral infections (aspirin component)","Hepatotoxicity with high doses","Renal impairment may require dose adjustment","Gastrointestinal adverse effects (e.g., nausea, dyspepsia, GI bleeding)","Coronary steal syndrome (dipyridamole) in patients with severe coronary artery disease","Pregnancy: avoid in third trimester due to premature closure of ductus arteriosus"] |
Loading safety data…
| FDA Category D. First trimester: aspirin may be associated with increased risk of neural tube defects and gastroschisis; dipyridamole use during pregnancy has limited data. Second trimester: generally considered lower risk, but aspirin may cause premature closure of ductus arteriosus. Third trimester: aspirin at high doses increases risk of premature closure of ductus arteriosus, oligohydramnios, and bleeding complications in mother and neonate; dipyridamole may theoretically increase bleeding risk. |
| Fetal Monitoring | Monitor maternal bleeding time, platelet count, and signs of bleeding. Fetal ultrasound for ductus arteriosus patency and amniotic fluid index in third trimester. Neonatal monitoring for bleeding complications after delivery. |
| Fertility Effects | High doses of aspirin may inhibit prostaglandin synthesis and impair implantation, potentially reducing fertility. Dipyridamole has no known significant effects on fertility. |
| Food/Dietary | Avoid alcohol; may increase risk of gastric bleeding and liver toxicity. No specific food restrictions, but maintain consistent intake of vitamin K-rich foods (e.g., leafy greens) if on warfarin concurrently. |
| Clinical Pearls | Combination product for secondary stroke prevention; aspirin inhibits cyclooxygenase, dipyridamole inhibits phosphodiesterase and adenosine uptake. Avoid in patients with hypersensitivity to NSAIDs or severe hepatic impairment. Monitor for bleeding risk, especially with concurrent anticoagulants. Contraindicated in patients with severe coronary artery disease due to risk of 'coronary steal' with dipyridamole. Titrate slowly to avoid headache, a common adverse effect. Use with caution in peptic ulcer disease or history of GI bleeding. |
| Patient Advice | Take this medication exactly as prescribed, usually twice daily with a full glass of water. · Do not crush or chew the extended-release capsules; swallow whole. · Avoid alcohol, aspirin-containing products, NSAIDs, and other blood thinners unless directed by your doctor. · Report any unusual bleeding, bruising, black stools, or persistent headache. · Stop use and seek medical attention if you experience signs of allergic reaction (rash, hives, swelling, difficulty breathing). · If you miss a dose, take it as soon as you remember. If close to next dose, skip the missed dose; do not double up. · Store at room temperature away from moisture and heat. |