The New Straits Times, October 18, 1996
Q: I was informed that aspirin and paracetomol are similar in terms of their uses and are available over-the -counter. Can you highlight the differences between the two?
A: Under normal recommended use, both aspirin and paracetamol are indicated for their anti-pyretic effects which leads to the reduction of increased body temperature normally encountered in cases of fever.
In addition, these drugs, are also used to achieve analgesia or pain-relieving effect. Thus the comparison between these drugs would be based on the two effects, namely the antipyretic and analgesic effects.
In terms of the antipyretic effects, various studies have been done to compare the onset or starting effect time and the duration of action for aspirin and paracetamol.
From these studies, it was concluded that both drugs were equally effective in the treatment of fever.
The similarity arises because both drugs mainly act on the thermoregulatory centre located in the hypothalamus of the brain.
In addition to this effect, aspirin is also believed to have additional effects in inhibiting the synthesis of the inflammatory mediator in the body which would also lead to an increase in the body temperature and prevent the release of microbial debris from the white blood cells which will be responsible in attacking foreign materials in the body.
For their comparative analgesic effects, clinical studies have shown that aspirin is more effective for clinical conditions requiring more potent anti-inflammatory activity such as rheumatic diseases and dysmenorrhea.
However, paracetamol does possess anti-inflammatory activity and was found to be useful in reducing swelling in minor inflammatory conditions such as inflammation occuring after a tooth extraction.
Due to the similar antipyretic and analgesic activities of aspirin and paracetamol, the selection of one drug over the other is dictated by safety and the clinical condition.
On the basis of safety, aspirin has a greater potential for toxicity than paracetamol.
For an example, the use of aspirin in children with certain viral diseases such as influenza A and varicella has been curtailed as aspirin has been associated with Reye's syndrome in children having these illnessess.
Reye's syndrome is characterised by vomiting, progressive central nervous system damage, signs of hepatic injury and hypoglycemia. Typically, the child with Reye's syndrome will be recovering from the viral infection and will abruptly develop intractable vomiting.
Subsequently, the child presents neurologic problems such as lethargy, disorientation, hostility, inability to recognise family members, incessant screaming, twitching and jerking.
From this stage the child can rapidly progress to coma and death within three to five days. On the other hand, paracetamol is preferred in clinical situations where patients are unable to tolerate aspirin such as patients with blood coagulation disorder, a history of peptic ulcer disease of asthma.
Another minor factor taken into consideration in the use of these drugs includes the potential of drug interactions when taken together with other drugs.
Drug interactions with aspirin are much more frequent as opposed to paracetamol especially during combined therapy with anticoagulant, ethanol, methotrexate (an anticancer drug) and phenytoin (an antiepileptic drug).
Thus, paracetamol is usually the drug of choice over aspirin but caution must be exercised in its use to achieve the maximium antipyretic effects and to avoid inadvertent over-dose.
