If a foley catheter is patent, everything is OK with the patient, how often should the catheter be changed?  New cath, new drainage bag?

As always, it is up to the doctor. Normally, the foley is changed once a month, unless the patient has some physical anomaly that makes the foley change too difficult. In that case, the doctor won't change it unless there is some signs of problems. If the foley care is done properly, then infections and other complications are rare. The drainage bag is usually changed every month. I have seen patients maintain indwelling foleys for several months without complications, thanks to good care and adequate hydration.

Thanks to all of you for your input!!!