You are a PA working in A&E and you are seeing a 67-year-old man who is complaining that he has been unable to urinate for the last 24 hours. He is complaining that he is in a lot of pain and that this has happened several times before. You insert a urethral catheter to relieve his symptoms, which is successful. Before he leaves, you need to discuss and decide on a treatment with the patient to prevent this occurring in the future. What do the nice guidelines suggest as the most appropriate medication to start for this patient?