|
Page: Toxicity of Low-dose Aspirin
Main article
| Home > Heart Problems > Toxicity of Low-dose Aspirin |
A recent review states: "....low-dose aspirin increases the risk of major bleeding 2-fold compared with placebo. However, the annual incidence of major bleeding due to low-dose aspirin is modest—only 1.3 patients per thousand higher than what is observed with placebo treatment. Treatment of approximately 800 patients with low-dose aspirin annually for cardiovascular prophylaxis will result in only 1 additional major bleeding episode." Further, "...the cost to prevent one major GI bleeding episode from aspirin in 1 year by substituting clopidogrel therapy would be $1,216,180..."
Aspirin
Aspirin is commercially synthesized using a two-step process. First, phenol (generally extracted from coal tar) is treated with a sodium base which generates sodium phenoxide, which is then reacted with carbon dioxide under high temperature and pressure to yield salicylate, which is acidified, yielding salicylic acid. This process is known as the Kolbe-Schmitt reaction.
Salicylic acid is then acetylated using acetic anhydride, yielding aspirin and acetic acid as a byproduct. It is a common experiment performed in undergraduate organic chemistry practicals, and generally tends to produce low yields due to the relative difficulty of its extraction from an aqueous state. The trick to getting the reaction to work is to acidify with phosphoric acid and heat the reagents under reflux with a boiling water bath for between 40 to 60 minutes.
The original synthesis of aspirin from salicylic acid involved acetylation with acetyl chloride. Unfortunately, the byproduct from this is hydrochloric acid, which is corrosive and environmentally hazardous. As described above, it was then later found that acetic anhydride was a better acylating agent, with the byproduct acetic acid formed, which does not have the unwanted properties of hydrochloric acid and can also be recycled. The salicylic acid/acetic anhydride method is commonly employed in undergraduate teaching labs.
Formulations containing high concentrations of aspirin often smell like vinegar. This is because aspirin can undergo autocatalytic degradation to salicylic acid in moist conditions, yielding salicylic acid and acetic acid.
The acid dissociation constant (pKa) for Acetylsalicylic acid is 3.5 at 25 °C. ASA, being a weak acid, dissociates as shown by the following reaction equation:
• Heart Problems - Aspirin...
• Heart Problems - Aspirin as Genericized Trademark...
• Heart Problems - Discovery...
• Heart Problems - Synthesis...
• Heart Problems - Mechanism of Action...
• Heart Problems - Indications...
• Heart Problems - Toxicity of Low-dose Aspirin...
• Heart Problems - Contraindications and Warnings...
• Heart Problems - Common Side-effects...
• Heart Problems - Interactions...
• Heart Problems - Overdose...
• Heart Problems - Research Into Cancer Prevention...
• Heart Problems - Aspirin in Pets...
|
|
Important notice:
The content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other
qualified health provider with any questions you may have regarding a medical condition.
|