Sorry, but no. Once the hearing loss has occurred, unless it's due to something temporary like congestion from a cold, it's permanent. However, hearing aids have improved immensely in design and effectiveness in recent years. He should talk to his doctor about what his options are.
Unfortunately, there is no medicine that can cure his hearing, because his ears may have been permanently damaged. However, there are antibiotics that can be prescribed for him to make his ears partially better.