Hi
Has your dad been fully investigated for the recurring infection. As a minimum I would recommend PSA, ultrasound of urinary tract , uroflowmetry, urine routine and culture and serum
creatinine.
Lupin injections are given for prostate cancer and not licenced just for shrinking the prostate to prevent infections.
If prostate causing blockage is the culprit then possibility of surgical intervention needs to be considered.