Acetylsalicylic acid

BRAND NAMES

• Bayer Aspirin: Available in various strengths, such as low-dose (81 mg) and regular-strength (325 mg).

• Bufferin: A buffered form of aspirin, designed to be gentler on the stomach.

• Ecotrin: Features a "safety-coated" or enteric coating to protect the stomach.

MECHANISM OF ACTION

Acetylsalicylic acid (ASA) works by blocking the synthesis of prostaglandins through non-selective inhibition of the COX-1 and COX-2 enzymes. Inhibiting COX-1 specifically leads to a reduction in platelet aggregation for approximately 7 to 10 days—the typical lifespan of a platelet. This occurs because the acetyl group of ASA irreversibly binds to a serine residue on the COX-1 enzyme, halting its activity. As a result, the production of prostaglandins, which are involved in pain signaling, is suppressed. 

PHARMACOKINETICS:

Absorption:

Acetylsalicylic acid, or aspirin, is primarily absorbed in the upper gastrointestinal (GI) tract through passive diffusion, with the stomach being a major absorption site. The drug's weak acid properties and its formulation play a key role in where and how quickly it is absorbed.

Distribution:

Once absorbed, acetylsalicylic acid (aspirin) is quickly distributed throughout the body, where it is extensively metabolized into its main active form, salicylic acid. This metabolite, like aspirin, is distributed to all tissues. The distribution of both aspirin and salicylic acid is affected by factors such as plasma protein binding, pH levels, and the administered dose.

Metabolism:

Acetylsalicylic acid, commonly known as aspirin, is rapidly metabolized in the body through a two-stage process. The first, and most rapid, step is the hydrolysis of aspirin into its primary active metabolite, salicylic acid.

Excretion:

Acetylsalicylic acid (aspirin) is primarily excreted by the kidneys following its metabolism. After being converted into its active metabolite, salicylic acid, it undergoes further breakdown into compounds such as salicyluric acid and glucuronide conjugates, which are eliminated in the urine.

PHARMACODYNAMICS

Acetylsalicylic acid (ASA), widely known as aspirin, produces its pharmacodynamic effects mainly through the irreversible inhibition of cyclooxygenase (COX) enzymes. Its specific actions—antiplatelet, pain relief (analgesic), anti-inflammatory, and fever reduction (antipyretic)—vary depending on the dosage and the particular COX isoform targeted.

ADMINISTRATION

The administration of acetylsalicylic acid (aspirin) varies widely depending on its intended use, the specific formulation, and the patient’s health status. It is available in multiple forms, such as regular tablets, chewable tablets, extended-release capsules, and rectal suppositories.

DOSAGE AND STRENGTH

Acetylsalicylic acid (aspirin) is available in a variety of strengths and its dosage varies depending on the condition being treated, the patient's age, and the formulation used. Common strengths include low-dose tablets of 75 mg, 81 mg, or 100 mg, which are typically used for cardiovascular prevention due to their antiplatelet effects. Standard-dose tablets of 325 mg are generally used for relieving pain, reducing fever, or treating mild inflammation. Higher strengths, such as 500 mg or 650 mg, may be used for more severe pain or inflammatory conditions.

DRUG INTERACTIONS

Acetylsalicylic acid, commonly known as aspirin, interacts with numerous medications, herbal supplements, and alcohol. These interactions can increase the risk of serious side effects, including severe bleeding, stomach ulcers, and kidney problems.

FOOD INTERACTIONS

Although there are no significant food interactions with acetylsalicylic acid (aspirin), it is generally advised to take it with food to help minimize stomach irritation and discomfort. The main concern is with alcohol consumption, as drinking alcohol while taking aspirin can heighten the risk of gastrointestinal bleeding. Therefore, it's recommended to limit or avoid alcohol while using aspirin.

CONTRAINDICATIONS

Acetylsalicylic acid (aspirin) should not be used in individuals with a known allergy to salicylates or other nonsteroidal anti-inflammatory drugs (NSAIDs). Its use is also contraindicated or requires extreme caution in the presence of certain medical conditions.

SIDE EFFECTS

Common side effects:

• Stomach pain or discomfort

• Indigestion or heartburn

• Nausea and vomiting

• Bruising more easily than normal

• Mild headache or drowsiness

• Gastrointestinal bleeding: Black, tarry stools; bloody vomit or vomit that looks like coffee grounds; or severe, persistent stomach pain.
• Severe allergic reaction: Hives, wheezing, swelling of the face, lips, tongue, or throat; or difficulty breathing.
• Hearing problems: Ringing in the ears (tinnitus) or hearing loss.
• Signs of stroke: Confusion, slurred speech, or weakness on one side of the body.

Serious side effects

OVER DOSE

An overdose of acetylsalicylic acid (aspirin), also known as salicylate poisoning, can occur from either a single large ingestion (acute overdose) or prolonged use of high doses (chronic overdose). It is a potentially life-threatening condition that requires prompt medical attention.

TOXICITY

Acetylsalicylic acid, or aspirin, induces toxicity known as salicylism by interfering with cellular metabolism, mainly by uncoupling oxidative phosphorylation within the mitochondria. Overdose may occur either as an acute event from a single large dose or as a chronic condition from repeated lower doses over time. The severity of toxicity and the symptoms experienced depend on the amount ingested and the age of the patient.