Auro Laboratories Limited offers Chlorzoxazone Active Pharmaceutical Ingredient. Auro Laboratories Limited is an ISO 9001:2000 accredited company. The Chlorzoxazone Active Pharmaceutical Ingredient is a muscle relaxant and used to relieve pain and stiffness caused by muscle strains and sprains. This Active Pharmaceutical Ingredient is used in combination with analgesics and physical therapy. It works by blocking nerve impulses [or pain sensations] that are sent to the brain.