Thanks for your query.Based on the facts that you have posted it appears that your friend has inflammation of the Urethra(Urethritis
Though routine urine and urine culture tests were negative it could bedue to inflammation of the mucus membrane of the urethra.
Please ask him to take broad spectrum antibiotics along with anti inflammatory medication like Diclofenac
twice daily .
Get the prescription of medicines from your family Physician.
Ensure to drink more water.To keep your urine dilute This will help to control dysuria
is an anti fungal drug and will not help in his case.