Aspirin (Acetylsalicylic Acid) 75mg is a low-dose, antiplatelet formulation primarily used for the secondary prevention of atherothrombotic events. It irreversibly inhibits platelet cyclooxygenase-1 (COX-1), preventing the synthesis of thromboxane A2, a potent platelet aggregator and vasoconstrictor. In the Indian context, it is a cornerstone therapy for cardiovascular prophylaxis, widely available and cost-effective.
Adult: 75mg to 150mg once daily. The standard dose for long-term secondary prevention in India is 75mg once daily. For ACS/PCI: A loading dose of 150-325mg (non-enteric) is given, followed by 75-100mg daily maintenance.
Note: Take with or after food to minimize gastric irritation. Swallow the tablet whole with a full glass of water. Do NOT crush or chew enteric-coated tablets. For rapid effect in ACS, a non-enteric coated tablet (150-325mg) should be chewed or dispersed in water. Timing: Usually taken in the evening or at bedtime based on some studies suggesting reduced morning platelet activity, but consistency is key.
Aspirin acetylates the serine residue (Ser529 in human COX-1) at the active site of the enzyme cyclooxygenase (COX), primarily COX-1 in platelets. This irreversible inhibition blocks the conversion of arachidonic acid to prostaglandin H2, the precursor for thromboxane A2 (TXA2) in platelets and prostacyclin (PGI2) in vascular endothelium. At low doses (75mg), it selectively inhibits platelet TXA2 production more than endothelial PGI2 due to first-pass hepatic deacetylation and the irreversible nature of platelet inhibition (platelets lack nuclei and cannot synthesize new COX).
Pregnancy: Category D in third trimester. Avoid in first and second trimesters unless clearly needed (e.g., for antiphospholipid syndrome). Low-dose (75mg) may be used under specialist supervision for pre-eclampsia prevention. High doses near term can cause premature closure of ductus arteriosus, delayed labor, and increased maternal/neonatal bleeding.
Driving: No effect on driving ability at this low dose. Dizziness or vertigo, if experienced, may impair ability.
| Warfarin / Acenocoumarol | Increased risk of major bleeding due to synergistic anticoagulant effect. | Major |
| Clopidogrel, Prasugrel, Ticagrelor | Synergistic antiplatelet effect (DAPT). Increases bleeding risk but is therapeutic for ACS/PCI. | Major (Therapeutic) |
| Ibuprofen / Naproxen (NSAIDs) | Competitive, reversible inhibition of platelet COX-1 can block aspirin's irreversible binding site, reducing its antiplatelet efficacy. Ibuprofen should be taken at least 2 hours after aspirin. | Major |
| Corticosteroids (e.g., Prednisolone) | Increase risk of GI ulceration and bleeding. | Moderate |
| Selective Serotonin Reuptake Inhibitors (e.g., Sertraline, Escitalopram) | Increased bleeding risk due to impaired platelet serotonin uptake. | Moderate |
| Methotrexate | Decreases renal clearance of methotrexate, increasing its toxicity (myelosuppression). | Major |
| ACE Inhibitors (e.g., Ramipril) | Aspirin may modestly attenuate the cardiovascular benefits of ACE inhibitors. | Moderate |
| Antacids | Can increase urinary pH, increasing renal excretion of salicylate, potentially reducing effect. | Minor |
| Probenecid | Decreases uricosuric effect of probenecid. | Moderate |
Same composition (Aspirin (75mg)), different brands: