Final answer:
The nurse should inform the patient to void every 4 hours to decrease the risk of urinary retention, as this is the correct teaching related to the side effects of an opioid analgesic.
Step-by-step explanation:
The correct information for the nurse to include when teaching an older adult client who has cancer and a new prescription for an opioid analgesic would be c. "You should void every 4 hours to decrease the risk of urinary retention." Opioid analgesics can cause urinary retention, and encouraging regular voiding can help mitigate this risk.
It is not expected for a client to sleep through the entire day as a result of taking opioid analgesics, so option a is incorrect. The nurse should also instruct a client on how to manage constipation, as tolerance to the drug does not typically lessen this side effect; therefore, option b is also incorrect. If a client experiences ringing in their ears, this is not a usual side effect of opioids and therefore may not necessarily indicate a need for dose reduction; option d is therefore incorrect.