2.12. Antipyretic Activity Test Using Yeast-Induced Hyperthermia in Rats

The antipyretic activity was evaluated with a fever induced by Brewer's yeast (Sigma 51475) following the established method in rats with some modifications [13]. The normal temperature was recorded before injection of Brewer's yeast using the rectal route using a digital probe thermometer for rats (BIOSEP®) to a depth of 3 cm into the rectum. Pyrexia was induced by subcutaneous injection of 20% w/v suspension of Brewer's yeast in distilled water at a dose of 10 mg/kg body weight. After 18 hours, the rise in rectal temperature was recorded, and only animals showing an increase in temperature of at least 0.6°C were selected for the study. The animals were randomly divided into six groups, each group containing five rats. Group 1 was treated with CMC-Na 0.5% (as negative control). Group 2 was treated with standard drug paracetamol at a dose of 150 mg/kg body weight [21]. Groups 3, 4, 5, and 6 were treated with AS201-01 tablets at a dose equal to 12.5, 25, 50, and 100 mg andrographolide/kg body weight, respectively. All treatments were administered orally. After the treatments, the rectal temperature of each animal was again recorded at 1 hour intervals up to 4 hours. The percentage reduction in pyrexia was calculated using the following formula:

where A is the normal temperature, B is the rectal temperature after 18 h of yeast injection, and Cn is the rectal temperature after 1, 2, 3, and 4 h.