Lorazepam metabolism/excretion

In contrast to chlordiazepoxide and diazepam, lorazepam and oxazepam are not metabolized into active compounds in the liver. Instead, they are excreted by the kidneys following glucuronidation. This is important because many alcohol-dependent patients have compromised liver function. Therefore, when treatment is initiated before the results of blood tests for liver function are known, as is often the case in outpatient clinics, lorazepam and oxazepam may be preferred. Patients with liver disease may still be treated with diazepam and chlordiazepoxide, but at lower doses. This can be accommodated with the loading technique, although hourly dosing with 5 mg of diazepam or 25 mg of chlordiazepoxide may be sufficient. 

As mentioned above, oxidative reactions will be rate-limiting in most instances. However, some medications are simply metabolized through conjugation. For example, benzodiazepines such as lorazepam are conjugated and excreted. The rate of conjugative reactions may be increased by OCs accelerating the elimination of these compounds because this reaction is rate-limiting [Yonkers and Hamilton 1995 Stoehr et al. 1984). 

At equipotent doses, all benzodiazepines have similar effects. The choice of benzodiazepine is generally based on half-life, rapidity of onset, metabolism, and potency. In patients with moderate to severe hepatic dysfunction, it may be useful to avoid benzodiazepines. All benzodiazepines are metabolized at various levels by the liver, which leads to an increased risk of sedation and confusion in hepatic failure. If it is necessary to prescribe this class of medication, lorazepam and oxazepam are reasonable choices because they are predominantly eliminated by renal excretion. 

Oxazepam (6) is formed during the metabolism of many other benzodiazepines, but its own metabolic profile is relatively simple. Like lorazepam, the major metabolic pathway is glucuronidation at the 3-hydroxy group followed by urinary excretion. Up to 80% of the dose is recovered from the urine as the glucuronide. The mean half-life of oxazepam is approximately 9 h (98). 

As with most benzodiazepines, lorazepam is highly bound to plasma proteins (over 85 percent). The serum half-life of lorazepam is approximately 12 to 15 hours. The drug undergoes hepatic metabolism and is rapidly conjugated to an inactive glucuronide. Excretion of the metabolite is primarily renal, with a small percentage excreted through the bile. 

The second group includes those that are metabolized only by conjugation to water-soluble glucuronides (subsequently excreted in the urine), which are pharmacologically inactive (e.g., lorazepam and oxazepam). 

Nefazodone appears to inhibit the oxidative metabolism of alprazolam, midazolam, triazolam and zopiclone by the cytochrome P450 isoenzyme CYP3A4 so that they accumulate in the body. Lorazepam is unaffected because it is primarily excreted as a conjugate. 

Elimination of lorazepam occurs by metabolism within the hver and renal excretion of the metabolites. Glucuronidation to form lorazepam-glucuronide is the major pathway for metabolism. Minor metabolites include a hydroxylated derivative, a quinazolinone derivative and a quinazoline carboxylic acid. Seventy... 

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