Used to treat anxiety disorders and seizure conditions, lorazepam and alprazolam are both medications belonging to the benzodiazepine class, which all serve similar functions. Important differences between these two medications dictate when each one is used in the medical practice. Both of these drugs have different half-lives, speeds of onset, and side effects which can make them more appropriate for certain conditions and patients.
The half-life of a medication is the time required for half of it to be metabolized and eliminated from the body in the form of waste after it is ingested. Lorazepam and alprazolam have similar average half-lives, around 10 to 11 hours, but the half-lives vary for each medication. Alprazolam's half-life tends to remain about the same for most people, whereas lorazepam's half-life can be as long as 16 hours. After days of consecutive dosing, lorazepam tends to remain in the body longer, making it the more useful medication of the two for treating chronic, severe anxiety.
Both medications have relatively rapid onset times, which is the time required for a medication to exert its effects after it is taken. The onset for alprazolam is slightly faster, however, which is why it is usually the medication of choice for treating panic disorder outside of medical settings. This disorder is marked by sudden, unpredictable panic attacks that usually necessitate rapid treatment. Orally-disintegrating alprazolam tablets are available to alleviate panic attacks, which greatly increase the drug's onset time to provide fast-acting relief.
Most benzodiazepines have similar side effects, and lorazepam and alprazolam are no exception. They do have slight variations from one another that can factor into their use. Lorazepam seems to have less of a potential for psychological dependence, due in part to its longer onset time. Physically, both lorazepam and alprazolam can lead to dependence if taken for more than four weeks at a time, but alprazolam seems to be more likely to cause rebound anxiety and other withdrawal symptoms if long-term, high doses are stopped suddenly.
Water solubility, or how well each medication can dissolve in water, also varies between these two drugs. Alprazolam, like most benzodiazepines, is not soluble in water, and therefore cannot be administered intravenously (IV). Lorazepam can be dissolved in water, and as such, can be given to patients in a hospital setting via IV. Due to its potential IV use, lorazepam is the drug of choice for treating seizures and panic attacks in a hospital setting.