Aspirin and Tylenol, the brand name for acetaminophen, are two of the most commonly used over-the-counter drugs. Not only are they considered quite safe under most circumstances, their popularity also stems from the fact that they are used to treat some of the most common ailments including headache, fever, toothache, and muscle pain. Despite the fact that there are some significant chemical differences between the two drugs, they share remarkable similarities in their bioactivity.
Anti-inflammatory Properties
Both aspirin and Tylenol are non-steroidal anti-inflammatory drugs, or NSAIDs, according to Drugs.com. Also in this category are naproxen and ibuprofen. Because of their anti-inflammatory action, both aspirin and Tylenol are commonly recommended to treat arthritis pain, as they don’t simply block the sensation of pain, they actually reduce swelling in the joint itself.
Analgesic Properties
Aspirin and Tylenol are both analgesic drugs, meaning they reduce the sensation of pain. They accomplish this by blocking the action of a specific set of enzymes, called cyclooxygenase enzymes, or COX. There are two types of COX enzymes: COX 1 and COX 2. Blocking COX 2 enzymes reduces the production of prostaglandins, which are molecules associated with pain and inflammation, notes Lauralee Sherwood, in her text “Human Physiology.” Blocking COX 1 enzymes doesn’t assist with analgesia; instead, COX 1 enzymes help maintain the integrity of the lining of the digestive tract, so turning these enzymes off can lead to gastric upset. Unfortunately, it is difficult to turn off one set of COX enzymes without affecting the other set, and as such, early NSAID drugs, like aspirin and Tylenol, block both types. As such, they have analgesic effects, but they also have potential for causing stomach irritation and ulcers.
Molecular Similarity
In the body, drugs exert their effects by binding to receptors. The drugs, called substrates, must fit into the receptors in a shape-specific way, similar to the way in which only the correct key can fit into, and open, a lock. In order to have the same effect in the body, different substrates must be able to bind to the same receptor, meaning they must have similar molecular shapes. As might be expected given their similar pharmaceutical activity, aspirin and Tylenol have similar molecular shapes. The “CRC Handbook of Chemistry and Physics” notes that each molecule consists of a core ring of six carbon atoms arranged in a hexagonal pattern. In both aspirin and Tylenol, two short “arms” of atoms are attached to the central ring. While these “arms” differ with regard to their exact atomic makeup, they’re very alike one another, giving the two molecules sufficiently similar shapes to fit into the same receptors in the body.
References
- Drugs: Aspirin
- Drugs: Tylenol
- “Human Physiology”; Lauralee Sherwood, Ph.D.; 2004
- "CRC Handbook of Chemistry and Physics"; David Lide; 1974
