Final answer:
The nurse must teach the patient to call his doctor if he cannot urinate.
Step-by-step explanation:
The priority teaching point the nurse must give to this patient in regard to his medication is to call his doctor if he cannot urinate. Benign prostatic hyperplasia (BPH) is a condition that can cause urinary retention in males. The anticholinergic drug prescribed to the patient may exacerbate this condition. Therefore, it is important for the patient to seek medical attention if he is unable to urinate.