Can i take 400mg(2 perles) of benzonatate at once,since taking the one perle of 200 mg isn't relieving my cough?

Not recommended: You are unlikely to get any additional benefit from a higher dose, but you may get unpleasant side effects. Consider a different cough suppressant, such as dextromethorphan or honey. If these are inadequate, your doctor may prescribe another medication depending on the cause of your cough.

Cough: 2 peerless will not do you any harm. However I do not know if it will help your cough. If it doesn't then you need to see a doctor and get some other treatment