Antipyretic and Analgesics:- An antipyretic is a during which is responsible for lowering the temperature of the feverish organism to normal but has no effect on normal temperature states. The central nervous system, especially the hypothalamus, plays an important role in maintaining the balance between the heat production and heat loss in order to regulate the body temperature. Hypothalamus is, thus, known as the thermostat of the body. In cases of fever, there still exists the balance between heat loss and heat production but the thermostat is only set at a higher temperature. The antipyretic drug helps to reset the thermostat at normal temperature. Heat production is not inhibited but heat loss is increased by increased peripheral blood flow which increases the rate of perspiration. This causes body to loss heat and subsequently lower the body temperature.

Aspirin is an important antipyretic. The other antipyretics are phenacetin, paracetamol, novalgin and phenyl butazone. Aspirin is absorbed from gastrointestinal tract. The stomach acid causes a partial hydrolysis of the easter. The easter circulates in the blood and further hydrolysis occurs into salicylic acid which is the active components. It causes several side effects. It may cause minute ulcers in the stomach and cause bleeding. Aspirin should not be taken empty stomach. Some persons are allergic to aspirin. The usual allergic reaction is rashes on skin, lowerin of blood pressure, profuse sweating, intense thirst, nausea and vomiting. Calcium and sodium salts of aspirin are more solube and less harmful. Aspirin is also used to prevent heart stroke because it acts as vaso dialator.

The derivatives of p amonophenol are used as antipyretic. The main limitation of these derivatives is that they may act on red blood cells and thus, they may be harmful in moderate doses.

It is highly toxic and hence not considered as a safe drug. Oxyphenyl butazone is less toxic and is used in place of phenylbutazone.