Nurofen Back Pain 300mg Sustained Release Capsules Nurofen Back Pain 300mg Sustained Release Capsules provide long-lasting relief from back-ache, rheumatic pain & muscular pain. They've been specifically designed to release the active ingredient throughout the day at the source of your pain for effective 12 hour relief. The active ingredient is ibuprofen, a Non-Steroidal Anti-inflammatory Drug (NSAID) that provides relief by changing the body's response to pain, swelling & high temperature.