Don't mind but its very strange that you have bought a nebuliser on your own for managing cough
of your 8 months old child. Now you are asking about the medication for nebulisation. Its not so easy dear.
Either trust your doctor because most of the respiratory infection are usually viral in origin and it takes its own time to resolve or if condition of baby is worsening or you have any doubt then consult some other specialist, but don't treat him yourself.