I've been on Lorazepam for over 10 yrs and have been told many times that Lorazepam does not have much effect on the liver compared to other benzosiazepines. And you can actual read about this online on many sites. Here are some sources. Therefore to say "These medications are completely metabolized in the liver" may cause some confusion...as benzodiazepins are metabolized differently.
http://psyweb.com/Drughtm/jsp/ativan.jsp
Ativan (Lorazepam) is an anti-anxiety agent (benzodiazepines,mild tranquilizer) used for the relief of anxiety, agitation and irritability, to relieve insomnia, to calm people with mania / schizophrenia and intravenously as a sedative and for nervous tension or to relieve anxiety prior to surgery. It has less of an effect on the liver than other benzodiazepines, making it better suited if you are taking birth control pills, anti-abuse drugs, propranolol, ulcer medications, or any other drug that affects the liver. Ativan (Lorazepam) may also be used to help in the prevention of severe alcohol withdraw symptoms (Delirium Tremens, or DTs), to treat amnesia, or in patients who are undergoing chemotherapy and have severe vomiting. It may be given to children to treat serial seizures by placing it under the tongue.
http://www.ncbi.nlm.nih.gov/pubmed/8700792
Lorazepam and oxazepam undergo only hepatic glucuronidation. Benzodiazepine oxidation is decreased in persons with liver disease and the elderly. Accumulation with resultant excessive sedation and respiratory depression may be significant when administering chlordiazepoxide or diazepam to patients with impaired oxidative metabolism. Lorazepam and oxazepam metabolism is minimally affected by age and liver disease. Chlordiazepoxide and diazepam are erratically absorbed by the intramuscular route. Lorazepam is predictably absorbed by the intramuscular route. Oxazepam is not available in parenteral form. Lorazepam appears to be the safest empiric choice among the various benzodiazepines for treating AWS in the elderly and in patients with liver disease, or those who require therapy by the intramuscular route.
http://thelastpsychiatrist.com/2006/05/liver_and_medications.html
There are two phases of liver metabolism.
Phase 1 occurs in smooth endoplasmic reticulum: reduction, oxidation, and hydrolysis. All the cytochrome P450 happens in Phase 1.
Phase 2 occurs in periportal region of portal triad: glucoronidation, acetylation, sulfation.
The trick of this is to understand that liver damage (cirrhosis, etc) affects Phase 1, not Phase 2.
This is why Ativan (lorazepam), Serax (oxazepam) and Restoril (temazepam)-- all metabolized primarily by Phase 2-- are favored in drinkers or cirrhotics. Also, renally metabolized or cleared drugs will not be as much affected (for example, Neurontin.)
http://www.ativansideeffects.net/
Luckily, lorazepam does not require oxidation (hepatic, the liver) to metabolize, so this makes it useful for alcoholics.