Bromhexine use has been noticed in poultry medicine but it should not be administered concurrently with tetracyclines. It should not be used in laying hens, the eggs of which are intended for human consumption. You can try guaiphenesin also which is also used widely in veterinary medicine.
Dera Neeraj! What I would do is to eradicate CRD or to put it to the lovast level possible. Could you give some more information about the flock you want to treat.