Short-acting barbiturate

Short-acting (eg, secobarbital [Seconal], pentobarbital [Nembutal]). The average duration of action of the short-acting barbiturates is 3 to 4 hours. 

Induction is a part of stage I anesthesia. It begins with the administration of an anestheticdrug and lasts until consciousness is lost. With some induction drugs, such as the short-acting barbiturates, this stage may last only 5 to 10 seconds. 

The ultra-short-acting barbiturates include methohexital sodium (Brevi-tal) and thiopental sodium (Pentothal). These agents are used as anesthetics and are administered intravenously. Barbiturates with short-to-intermediate duration of action are used for their sedative-hypnotic effect in the treatment of anxiety. These medications include amobarbital (Amytal), butabarbital (Butisol), sodium pentobarbital (Nembutal), and secobarbital (Seconal). 

Secobarbital exhibits the same pharmacologic properties as other members of the barbiturate class. Most nonmedical use is with short-acting barbiturates, such as secobarbital. Although there may be considerable tolerance to the sedative and intoxicating effects of the drug, the lethal dose is not much greater in addicted than in normal persons. Tolerance does not develop to the respiratory effect. The combination of alcohol and barbiturates may lead to fatalities because of their combined respiratory depressive effects. Similar outcomes may occur with the benzodiazepines. Severe withdrawal symptoms in epileptic patients may include grand mal seizures and delirium. 

Aspirin and acetaminophen are also available by prescription in combination with a short-acting barbiturate (butalbital). No randomized, placebo-controlled studies support the efficacy of butalbital-containing formulations for migraine. 

Clinical reports of patients who underwent chloroform anesthesia indicated that premedication with morphine caused serious respiratory depression when chloroform was co-administered. Thiopentone (thiopental Na, an ultra-short-acting barbiturate anesthetic) was associated with increased incidences of hypotension in chloroform-anesthetized patients (Whitaker and Jones 1965). 

B arbitur ates are metabolized in the liver via hydroxylation and glucuronide conjugation. Short-acting barbiturates are excreted in the urine as metabolites for about one to four days, while long-acting barbiturates are excreted for two to three weeks. 

Anaesthesia The ultra short acting barbiturates produce general anaesthesia (details are given in chapter General anaesthetics ). 

They are well absorbed from the GIT. They are widely distributed in body. Rate of entry into CNS is dependent on lipid solubility. Ultra short acting barbiturates are highly lipid soluble and quickly enter the brain. Redistribution to various tissues terminate their action and they are slowly released from the tissues and gradually metabolised in the liver. They are partly metabolised and partly excreted unchanged in urine. 

For general anaesthesia Ultra short acting barbiturates are used. 

Thiopental is a short-acting barbiturate commonly used for induction of anesthesia. The general pharmacology of the barbiturates is discussed in Chapter 22 Sedative-Hypnotic Drugs. 

Barbiturates are classified according to their duration of action (Figure 9.7). For example, thiopental [thye oh PEN tal], which acts within seconds and has a duration of action of about 30 minutes, is used in the intravenous induction of anesthesia. By contrast, phenobarbital [fee noe BAR bi tal], which has a duration of action greater than a day, is useful in the treatment of seizures (see p. 148). Pentobarbital [pen toe BAR bi tal], secobarbital [see koe BAR bi tal] and amobarbital [am oh BAR bi tal] are short-acting barbiturates, which are effective as sedative and hypnotic (but not antianxiety) agents. 

Anesthesia Selection of a barbiturate is strongly influenced by the desired duration of action. The ultra-short-acting barbiturates, such as thiopental, are used intravenously to induce anesthesia. 

Rapid induction of anesthesia (short-acting barbiturate)... 

Stage II—excitement The patient experiences delirium and violent combative behavior. There is a rise and irregularity in blood pressure. The respiratory rate may be increased. To avoid this stage of anesthesia, a short-acting barbiturate, such as sodium pentothal, is given intravenously before inhalation anesthesia is administered. 

For the past 40 and more years, a modified form of ECT has been standard, involving sedation with a short-acting barbiturate, muscle paralysis with a curare derivative or similar drugs that prevent activation of the muscles of the body, and artificial respiration with oxygen. The purpose... 

In large doses, injected intravenously, it would bum and hurt horribly, because it s a salt and because it instantly throws off the chemical balance of the blood with which it comes into contact. It makes all muscles lock up in extreme contraction that would hurt unbearably. It wouldn t get to all muscles when a prisoner is being killed with it, however. Since the heart is a muscle and it pumps the blood -- the minute that massive dose of potassium salt hits the heart, one would be history and that would be as far as it would travel. "In lethal injection, three chemicals are used to kill. First, sodium pentothal (its trade name) or thiopental sodium (its chemical name). Then one minute later they inject pavulon. One minute later the potassium chloride. Pentothal is a short acting barbituric acid (barbiturate used in anaesthesia) and is commonly called "truth serum" as it s used in narcoanalysis. It knocks one out. It s a hypnotic. Pavulon is a curare derivative which locks up the lungs so one can t breathe. 

Additive psychoactive effects sought by users may be achieved by combinations of cannabis and short-acting barbiturates, but at the same time the ability of THC to induce microsomal enzymes will increase the rate of metabolism of barbiturates and so reduce the additive effects (127). 

Finally, there are very short-acting barbiturates that produce almost immediate unconsciousness when injected intravenously. Thiopental (Pcntothal) is the main example dentists and doctors use it as an anesthetic for surgical operations. Since it wipes out awareness so fast and leaves no memory of the experience, no one takes it for fun. 

When people talk about taking downers they usually mean the short-acting barbiturates or a few similar drugs that will be mentioned later. All of these substances are like alcohol, and most of the statements in the alcohol section apply to downers as well. Sleeping pills can make people feel and look drunk, can leave... 

As noted, the barbiturates once were used extensively as sedative-hypnotic drugs, but except for certain specialized uses they now have been replaced by the safer benzodiazepines. Short-acting barbiturates still are used to produce anesthesia. Other current uses include emergency treatment of convulsions and prevention of seizures in persons with certain types of epilepsy (Perrine, 1996). 

Thiopental Sodium, USP. Thiopental. sodium, sodium S-ethyl-S-(l-methylbutyl)-2-lhiobarbilurale (Pentothal Sodium). is the mo.st widely u.sed ultra-short-acting anc.sthctic barbiturate. Additionally, the compound is the prototype for the ultra-short-acting barbiturates. Most discussions of how structure influences duration of action in this group of agents relate specifically to it. The compound s onset of action is about equal to the time required for it to travel to the brain from the site of administration. Consciousness is regained within 30 minutes. 

The short-acting barbiturates are used for short-term treatment of insomnia, anxiety, psychosis, preoperative sedation, control of seizures, and anesthetics. Short-acting barbiturates are also used as drugs of abuse. Barbiturate use has dramatically decreased since the 1970s with the introduction of benzodiazepines. 

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