Barbiturates

Medicinal Use and Alpine

Barbiturates are much less commonly prescribed now than they were before the introduction of benzodiazepines. There are more than a dozen different barbiturates available by prescription. Like the benzodiazepines, they range from ultra short-acting to long-acting. Their medicinal use depends on their duration of action. Ultra short-acting barbiturates (thiopental, methohexital) are used to induce surgical anesthesia. Short- to intermediate-acting barbiturates (amobarbital, butabarbital, butalbital, pentobarbital, secobarbital) are used as sedatives and hypnotics. Because of their rapid onset and short duration of action, these barbiturates are most frequently abused. Butalbital is frequently prescribed for tension headaches, usually in combination with salicylates (Fiorinal) or acetaminophen (Fioricet). Long acting barbiturates (mephobarbital, phenobarbital) are used primarily for their anticonvulsant properties and are rarely abused. Phenobarbital is also present in some medication used to treat gastrointestinal disorders Eg: Bellaspas, Donnatal, and Spastrin), but is no longer available in OTC preparations.

Barbiturates have a low therapeutic index and have resulted in fatal overdoses and suicides. They have a high potential for abuse and used to be widely available on the street. Common street names, depending on the barbiturate, include Black Beauties, Blue Birds (amobarbital), Downers, Goofballs, Pink Ladies, Red Devils (secobarbital), and Yellow Jackets (pentobarbital). Symptoms of intoxication and overdose are consistent with the acute CNS depressant effects of ethyl alcohol. Unlike the benzodiazepines, high doses of barbiturates produce generalized neuronal depression, respiratory depression, and hypotension.

Metabolism and Analytical issues

Long-acting barbiturates, such as phenobarbital, are excreted in the urine primarily as the parent drug and are not extensively metabolized. Short and intermediate-acting barbiturates are more extensively metabolized by the liver and are excreted in the urine as hydroxylated, dealkylated, and conjugated metabolites. Detection tunes in the urine vamp depending on the barbiturate. Phenobarbital can be detected for several weeks after chronic therapeutic use. Intermediate-acting barbiturates may be detected 2 to 4 days after use, while some short- and ultra short-acting barbiturates if detected, may only be present in the urine for a day or less.

The immunoassays for barbiturates are designed to detect secobarbital, usually with a screening cutoff of 200 or 300 ng/mL. Cross-reactivity to other barbiturates varies. Many of the variables described for the confirmation of benzodiazepines apply to the barbiturates as well. However, there is somewhat greater uniformity in barbiturate confirmation procedures. The most common barbiturates included in a confirmation panel are amobarbital, butalbital, pentobarbital, phenobarbital, secobarbital, and less often, butabarbital. Generally, the screening cutoff is higher than the confirmation cutoff.

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