Unintended Effects of Aspirin
Aspirin is associated with significant gastrointestinal bleeding risks with an odds ratio of 1.59 (95% CI 1.32-1.91), which should be carefully considered before initiating therapy, especially in high-risk patients. 1
Gastrointestinal Effects
- The most commonly reported adverse effects of aspirin are nonspecific gastrointestinal symptoms, including abdominal pain, dyspepsia, nausea, and vomiting 1
- Gastrointestinal bleeding is the most common serious adverse event, with an increase of 0.29 events per 1,000 person-years of aspirin exposure 1
- The risk of GI bleeding is dose-dependent, with higher doses associated with increased risk 1
- Enteric-coated or buffered preparations do not clearly reduce the adverse gastrointestinal effects of aspirin 1, 2
- Some studies suggest enteric-coated aspirin may actually be more injurious to small bowel mucosa than buffered aspirin 2
- Low-dose aspirin (75-325 mg/day) increases the risk of upper GI bleeding with a standardized incidence rate ratio of 2.6 (95% CI 2.2-2.9) 3
- Small bowel injury can occur with chronic use, including multiple petechiae, loss of villi, erosions, and ulcers, with some patients developing circumferential ulcers with stricture 2
Bleeding Risks
- Intracranial bleeding is associated with aspirin use (OR = 1.27; 95% CI 0.98-1.66), with an absolute risk increase of 0.1 events per 1,000 person-years 1
- Bleeding events correlate with dose and increasing age 1
- The estimated adjusted incidence rate ratio for major bleeding events increases by 1.05 (95% CI 1.05-1.05) with each year of age 1
- Men have twice the risk for serious gastrointestinal bleeding compared to women 1
- Combined use of low-dose aspirin with other NSAIDs significantly increases bleeding risk (standardized incidence rate ratio of 5.6; 95% CI 4.4-7.0) 3
Risk Factors for Bleeding Complications
- Advanced age (particularly >60 years) 4
- History of peptic ulcer or upper GI bleeding 1
- Concomitant use of NSAIDs (including COX-2 selective NSAIDs) 1, 3
- Concomitant use of anticoagulants 1
- Helicobacter pylori infection 5
- Uncontrolled hypertension 1
- Severe liver disease 1
- Renal failure 1
- Bleeding disorders 1
- Low platelet count (thrombocytopenia) 1
Other Adverse Effects
- Aspirin may cause severe allergic reactions including hives, facial swelling, asthma (wheezing), and shock 4
- Reye's syndrome risk in children and teenagers recovering from chicken pox or flu-like symptoms 4
- Esophageal injuries (esophagitis and stricture) have been reported 6
- Aspirin is associated with variceal bleeding episodes in patients with cirrhosis 6
- Colonic complications can include perforation, bleeding, collagenous colitis, and anorectal stenosis (with suppositories containing aspirin) 6
Risk Mitigation Strategies
- For GI symptoms and prophylaxis for bleeding, clinical management may include co-administration of a proton pump inhibitor (PPI) or H2 blocker 1, 5
- Eradication of H. pylori appears to reduce the risk of upper GI side effects, especially in high-risk patients 5
- Use the lowest effective dose of aspirin (approximately 75-81 mg/day) as it seems as effective as higher dosages while potentially reducing side effects 1
- Regular monitoring for signs of bleeding is recommended, especially in high-risk patients 1
- Patients should be educated about signs and symptoms of GI bleeding (dark stools, vomiting blood, bright red blood per rectum, syncope, lightheadedness) 1
Contraindications
- Aspirin allergy or intolerance 1
- Active peptic ulcer 1
- Bleeding disorders 1
- Recent history of GI or intracranial bleeding 1
- Renal failure 1
- Severe liver disease 1
- Low platelet count (thrombocytopenia) 1
- Children and teenagers with or recovering from chicken pox or flu-like symptoms (due to Reye's syndrome risk) 4
When considering aspirin therapy, clinicians must carefully weigh these potential adverse effects against the cardiovascular benefits, particularly in patients with multiple risk factors for bleeding complications.