The nurse is preparing to administer meperidine (Demerol), a…

The nurse is preparing to administer meperidine (Demerol), an opioid analgesic, and promethazine (Phenergan), which is an antiemetic and antihistamine. When given together, the clinical effect of sedation for these two drugs is greater than the sum of the individual effects when given alone. This is an example of: