What is the purpose of stress testing in stability studies?

Stress testing of the drug substance can help identify the likely degradation products, which can in turn help establish the degradation pathways and the intrinsic stability of the molecule and validate the stability indicating power of the analytical procedures used. The nature of the stress testing will depend on the individual drug substance and the type of drug product involved.

What countries comes under climatic zone ivb?

Brazil, Cuba, China, Brunei, Cambodia, Indonesia, Malaysia, Myanmar, Philippines, Singapore, Thailand

According to WHO guidelines what is the storage condition of climatic zone iva and zone ivb?

Zone IV a: 30°C and 65% RH (hot and humid countries)

Zone IV b: 30°C and 75% RH (hot and very humid countries)

Forced degradation( stress testing ) & accelerated stability testing are same?

Forced degradation and stress testing are not same. Stress testing is likely to be carried out on a single batch of the drug substance. The testing should include the effect of temperatures (in 10°C increments (e.g., 50°C, 60°C) above that for accelerated testing), humidity (e.g., 75 percent relative humidity or greater) where appropriate, oxidation, and photolysis on the drug substance. The testing should also evaluate the susceptibility of the drug substance to hydrolysis across a wide range of pH values when in solution or suspension. Photo stability testing should be an integral part of stress testing.