Which of the following is a commonly used anesthetic agent?

Ketamine is a commonly used anesthetic agent primarily due to its unique properties as a dissociative anesthetic. It produces a trance-like state while providing pain relief, sedation, and amnesia. This makes it particularly valuable in a variety of medical settings, such as in emergency medicine for quick sedation and pain relief without the loss of respiratory drive, which is an important benefit in patients who may have compromised respiratory function.

In contrast, the other options listed primarily serve different purposes. Lorazepam is primarily used as an anxiolytic and sedative but is not an anesthetic. Meperidine is an opioid analgesic used to relieve pain rather than as an anesthetic agent. Alprazolam is also an anxiolytic used for anxiety and panic disorders, again not used for anesthesia. Therefore, ketamine is distinguished as an agent specifically designed for inducing anesthesia, making it the correct answer in this context.