16th October 2009, 05:40 AM
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Member
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Join Date: Jul 2008
Location: usa
Posts: 58
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Barbiturates
Barbiturates are sedative drugs that are derived from barbituric acid and have the ability to depress the central nervous system and act especially on the sleep center in the brain, thus their sedative and sometimes hypnotic effects.
The method of synthesis for thousands of barbital analogs involves the reaction of urea with various derivatives of malonic acid, usually a diethyl ester of a dialkyl-substituted malonic acid.
The barbiturates are usually administered as the sodium salts. The N-H bonds are acidic and although barbituric acid itself is inactive, a range of activities is obtained that varies with the groups at R and R1. Activity and toxicity both increase with the size of the groups. Branching and unsaturation decrease the duration of action.
Barbiturates have been used in sleeping pills, but in recent years several other compounds also have been introduced for this purpose. Barbiturates induce a feeling of relaxation, usually followed by sleep, and have been used to provide temporary respite in times of unusual emotional stress, but they will only prolong the stress and patient reliance on the drugs is common.
The maximum therapeutic index (tolerated dose/minimum effective dose) is highest when the two groups have a total of 6 to 10 carbons. Major drawbacks of their use are their habit formation and their high toxicity when alcohol is present in the bloodstream.
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