Final answer:
The hypermetabolic reaction caused by concurrent use of phenelzine and meperidine is due to serotonin syndrome, which can be characterized by symptoms such as vertigo, loss of balance, and polyneuropathy.
Step-by-step explanation:
The concurrent use of phenelzine (a monoamine oxidase inhibitor, or MAOI) and meperidine (an opioid analgesic) can lead to a hypermetabolic reaction due to serotonin syndrome. This potentially life-threatening condition occurs when there is an excess of serotonin in the body, and it can cause symptoms such as vertigo, loss of balance, and polyneuropathy. The combination of these drugs is particularly dangerous because meperidine has serotonergic properties which can cause serotonin to accumulate when combined with MAOIs like phenelzine, which inhibit the breakdown of serotonin.