Medications are unlikely to help. It's better to strictly reduce the intake of oral liquids from 6pm onwards till morning. Ensure that he passes urine just before going to bed. Wake him up around 2-3 hours after he goes to sleep (make sure he's totally awake) and make him go to toilet and pass urine. If you do this strictly for about 4 weeks, his brain gets trained to wake him up if he gets an urge to void and he will stop bed wetting. If this doesn't work out, get a physical consultation with urologist.